The effluent streams from individual slaughtering operations were segregated based on the degree of similarity and were treated separately. The wastewater from lairage and paunch sections was dominant in suspended solids (SS: 6,000–25,000 mg/L) and was separated using a hydrasieve (500 μm) and externally fed rotary drum filter (EFRDF, 200 μm), respectively. The SS removal efficiency of the hydrasieve and EFRDF was 75% and 55%, respectively, and remaining solids were removed through a primary clarifier. The fats, oils and grease (FOG: 12,000–35,000 mg/L) containing streams from the hide fleshing, rendering, intestine, and tripe washing were routed through a skimming tank. The SS and FOG removal efficiencies through the skimming tank were 75% and 90%, respectively. Any FOG remaining after the skimming tank was removed using dissolved air flotation which achieved 95% FOG removal. In addition, the efficiency of chemical oxygen demand removal through the primary treatment system was more than 80%. The effluent obtained after primary treatment was SS and FOG ≤ 200 and 100 mg/L. The segregation of streams and their separate treatment offered benefits such as resource recovery, reduced waste load on downstream secondary treatment and overall ease in slaughterhouse wastewater treatment.

  • Segregation of streams and the removal of dung solids (TSS) and fats, oils, and grease (FOG) through multi-intervention approach is highly efficient.

  • Hydrasieve-drum filter-primary clarifier ensures TSS removal to less than 200 mg/L.

  • Skimming tank–DAF ensures FOG removal between 80 and 100 mg/L.

  • Segregation of streams based on the nature of similarity and separate treatment is key to managing the slaughterhouse wastewater.

The efficient primary wastewater treatment is the most crucial step in determining the overall success of any industrial effluent treatment plant (ETP). The primary wastewater treatment has two basic objectives: (1) separation of suspended solids (SS) and reduction of biochemical oxygen demand (BOD); and (2) utilization of separated materials for making commercial products (USEPA 2002). One of the necessary steps while dealing with slaughterhouse wastewater is its effective primary wastewater treatment. SS and fats, oils, and grease (FOG) contribute a major burden in slaughterhouse wastewater. Several researchers have reported the problems encountered due to the ineffective primary treatment of slaughterhouse wastewater. Anaerobic digestion is a versatile process for treating wastewater with a high organic concentration. Still, the accumulation of SS and FOG may lead to loss of sludge (biomass washout), limit the chances of operating at high organic loading, and deteriorate the specific methanogenic activity in upflow anaerobic sludge blanket (UASB) and anaerobic suspended biomass reactors. Chocking and clogging due to SS hinder the performance of anaerobic fixed film reactors treating slaughterhouse wastewater (Sunder & Satyanarayan 2013). Miranda et al. (2005) stated that an oil and grease/chemical oxygen demand (COD) ratio above 20% in the influent causes low-performance efficiency, biomass washout and a failure of the UASB system. Thus, the performance of these anaerobic technologies relies on the effective removal of SS and FOG. High FOG content in wastewater has an adverse effect because of its insoluble nature, slowing down the degradation rate. FOG may also prove problematic because of its capacity to form scum and coat surfaces. Moreover, SS and FOG are the prime reasons for the fouling of membranes used in the filtration process (Ghaffour 2004). Effective primary treatment of slaughterhouse wastewater is therefore essential to ensure performance of downstream secondary biological treatment systems.

The target pollutants in the primary treatment of slaughterhouse wastewaters are SS and FOG. Table 1 presents the summary of the various solid–liquid separation equipment used to remove SS from the effluent. Fleming & Macalpine (2003) evaluated the screw press for swine manure treatment using a screen with an opening of 0.25 mm with axial wire. It was found that because of the low solid content in the influent, it was difficult to develop a good liquid seal in the solid discharge; as a result, the dry matter (DM) percentage (%) in the effluent was more (0.92%) than the influent (0.84%). A vibratory screen with a 0.212-mm screen opening was used for the influent from the dairy farm, which had a DM content of less than 1.85%. The DM removal efficiency of nearly 11.89% was achieved. However, flow rates had to be reduced over time as the solid level rose while operating the vibratory screen (Fleming & Macalpine 2003). Fernandes et al. (1988) developed continuous belt microscreening to manage swine wastewater using a belt made of a filter medium with a 100-μm opening and involved continuous cleaning by airflow. It was operated at a hydraulic loading rate (HLR) of 0.145 m3/m2·min. The efficiency of the continuous belt microscreening unit increased with an increase in initial SS concentration in the influent slurry. The DM removal efficiency of 53% for the initial DM of 4.7% was increased to 60% for the initial DM of 8% in the influent slurry.

Table 1

Performances of solid–liquid separation equipment

Solid–liquid separation equipmentScreen SizeType of slurryAverage flow in m3/hInfluent DM (%)Effluent DM (%)% RemovalSeparated solids DM (%)Power consumptionaReference
Screw press 0.25 mm axial wire screen Swine manure 6.12 0.84 0.92 – 6.41 0.239 kWh/m3 Fleming & Macalpine (2003)  
4.98 2.2 2.43 – 34.8 0.625 kWh/m3 
Vibratory screen 0.212 mm Dairy manure 1.56 1.85 1.63 11.89 7.27 0.129 kWh/m3 
Continuous belt microfiltration Filter fabric opening size: 100 micron Swine manure HLR of 0.145 m3/m2·min 4.7 2.2 53 14–18 Electricity is required for the conveyor belt and air knife for cleaning Fernandes et al. (1988)  
 3.2 60 
Screw press 0.50 mm screen opening Dairy farm 6.6 8.32 ± 0.46 5.06 ± 0.33 39.18 24.6 ± 0.67 – Gooch et al. (2005)  
2.25 mm screen opening Dairy farm 12.75 5.50 ± 0.37 5.19 ± 0.40 0.05 29.3 ± 2.48 – 
0.75 mm screen opening Dairy farm 11.21 9.96 ± 0.52 4.93 ± 0.28 50.5 25.3 ± 1.12 – 
Decanter centrifuge – Anaerobically digested livestock slurry 2.3 54 21.4 Nearly 1 kWh/m3 Giorgia (2013)  
2.3 54 21.6 
2.4 52 21.9 
Brushed screen separator 1.6 mm screen opening Cattle slurry – 60.4 g/kg 33 g/kg 45 129.9 g/kg 0.075 kWh/m3 Gilkinson & Frost (2007)  
Decanter centrifuge Bowl Speed 4,500 rpm Cattle slurry – 59.7 g/kg 17.9 g/kg 70 213.4 g/kg Nearly 1.5 kWh/m3 
Inclined screen 2.5 mm Dairy farm – 6,000–7,000 mg/L 2,900 mg/L 51–58 131 g/L – Wright (2018
Solid–liquid separation equipmentScreen SizeType of slurryAverage flow in m3/hInfluent DM (%)Effluent DM (%)% RemovalSeparated solids DM (%)Power consumptionaReference
Screw press 0.25 mm axial wire screen Swine manure 6.12 0.84 0.92 – 6.41 0.239 kWh/m3 Fleming & Macalpine (2003)  
4.98 2.2 2.43 – 34.8 0.625 kWh/m3 
Vibratory screen 0.212 mm Dairy manure 1.56 1.85 1.63 11.89 7.27 0.129 kWh/m3 
Continuous belt microfiltration Filter fabric opening size: 100 micron Swine manure HLR of 0.145 m3/m2·min 4.7 2.2 53 14–18 Electricity is required for the conveyor belt and air knife for cleaning Fernandes et al. (1988)  
 3.2 60 
Screw press 0.50 mm screen opening Dairy farm 6.6 8.32 ± 0.46 5.06 ± 0.33 39.18 24.6 ± 0.67 – Gooch et al. (2005)  
2.25 mm screen opening Dairy farm 12.75 5.50 ± 0.37 5.19 ± 0.40 0.05 29.3 ± 2.48 – 
0.75 mm screen opening Dairy farm 11.21 9.96 ± 0.52 4.93 ± 0.28 50.5 25.3 ± 1.12 – 
Decanter centrifuge – Anaerobically digested livestock slurry 2.3 54 21.4 Nearly 1 kWh/m3 Giorgia (2013)  
2.3 54 21.6 
2.4 52 21.9 
Brushed screen separator 1.6 mm screen opening Cattle slurry – 60.4 g/kg 33 g/kg 45 129.9 g/kg 0.075 kWh/m3 Gilkinson & Frost (2007)  
Decanter centrifuge Bowl Speed 4,500 rpm Cattle slurry – 59.7 g/kg 17.9 g/kg 70 213.4 g/kg Nearly 1.5 kWh/m3 
Inclined screen 2.5 mm Dairy farm – 6,000–7,000 mg/L 2,900 mg/L 51–58 131 g/L – Wright (2018

aPower consumption excludes the cost of pumping.

DM, dry matter.

Gooch et al. (2005) assessed the performance of the screw press for three different dairy farms and found that its performance increased as the input solid concentration in the influent stream increased. DM percentage removal efficiency was 50.5% when the initial DM% in the influent was 9.96%, and it reduced to 39% when the DM% in the influent stream was nearly 8.32%. Although the screw press performed satisfactorily with a higher DM% in the influent stream, it is essential to have a screen opening of appropriate size. Gooch et al. (2005) found only 0.05% DM removal efficiency with the screen opening of 2.25 mm while operating a screw press for one of the dairy farms with an average flow of 12.75 m3/h. Giorgia (2013) assessed the dewatering of anaerobically digested livestock slurry using a decanting centrifuge. The initial solid concentration in the influent slurry was 5%, and that of the outlet was between 2.3% and 2.4%. A solid removal efficiency of 52–54% was gained for a feed flow rate of 4–6 m3/h. The solid concentration in separated solids was 21.7–29%. The electricity consumption of the decanting centrifuge was 1 kWh/m3, considerably more than other solid–liquid separation technologies. The author also demonstrated that the decanting centrifuge's performance could be further enhanced by adding polymers in the influent slurry. Gilkinson & Frost (2007) also carried out a similar study to check the vibratory screen performance and decanting centrifuge to handle cattle slurry. The vibratory screen achieved solid removal efficiency of 45% compared to the centrifuge which achieved 70% solids removal efficiency. However, the power requirement for the vibratory screen was only 0.075 kWh/m3 and that for centrifuge was nearly 1.5 kWh/m3.

It was observed that regardless of the different solid–liquid separation technologies used to manage livestock slurry, DM removal efficiency was around 50%. At the same time, it is equally important to consider the power required to run these separation systems. Power requirement for the decanter centrifuge was higher (1.5 kWh/m3) (Gilkinson & Frost 2007), and for the screw press, it was 0.239–0.625 kWh/m3 (Fleming & Macalpine 2003). One of the crucial parameters that decide the success of the solid–liquid separation systems is the pore size of the screen. As shown by Fernandes et al. (1988) using a continuous belt microfiltration unit with a filter fabric with an opening size of 100 μm, DM removal efficiency of 53–60% was achieved. In a particle-size distribution study of cattle slurry carried out by Salehion et al. (2013), it was found that a 0.7-mm sieve retained 87.6% DM. Wright (2018) found that 78% of the total mass was larger than 0.63 mm, and 51% of the total mass was larger than 2.5 mm; as a result, they used a simple inclined screen with an opening of 2.5 mm and achieved SS removal efficiency of 51–58%. It is imperative to mention here that the SS removal efficiency in the case of Wright (2018) can be further improved by using screens with smaller openings. In the market, inclined and rotary drum screens are available with opening sizes starting from 100 to 1,000 μm.

Moreover, the size and composition of particles from livestock/dairy farms/lairage and paunch sections vary with animal species, diet and period for which the wastewater is stored because anaerobic bacteria start degrading dung particles (Møller et al. 2002). The authors believe that to manage wastewater from the lairage and paunch section, simple solid–liquid separation equipment such as a hydrasieve, or an externally or internally fed rotary drum filter with suitable screen size may prove better than more sophisticated equipment such as a centrifuge, screw press, or vibratory screen, etc.

Several researchers have also conducted studies to evaluate dissolved air flotation (DAF) performance for treating effluent from a slaughterhouse using both laboratory and full-scale experiments. Ross et al. (2000) assessed the DAF unit's performance to treat poultry rendering wastewater with very high SS (43,706 mg/L) and FOG (18,568 mg/L). The DAF was operated with pH adjustment using sulphuric acid and cationic polymer dosing. It was operated at the air to solid (A/S) ratio of 0.0006, which is nearly 1/10th the minimum value of the A/S ratio reported by Qasim (1998) and Metcalf & Eddy (2003). Both SS and FOG removal efficiency of more than 98% was achieved. Nardi et al. (2008) evaluated the performance of DAF with full flow pressurization. SS and FOG removal efficiencies were 43 ± 15% and 49 ± 8%, respectively, when operated with chemical dosing of 24 mg Al3+/L and 1.5 mg anionic polymer. The same DAF unit with full flow pressurization was upgraded to operate with the recycle flow pressurization with a pressure of 4.5 kg/cm2.

Upgraded DAF under the same chemical dosing resulted in SS and FOG removal efficiencies of 74% and 99%, respectively. Generally, fat removal efficiencies in DAF are more than that of the SS removal efficiencies for two reasons: (1) the nature of fat to travel upward; and (2) its hydrophobic nature (Kitchener & Gochin 1981). Lovett & Travers (1986) measured the performance of a laboratory-scale DAF unit that was treating abattoir wastewater and found that maximum removal efficiencies of SS and FOG were 70% and 95%, respectively, and occurred at influent SS of 1,200–2,105 mg/L and A/S ratios of 0.05–0.06. The study also showed that at low A/S ratios, solid removal occurred by both settling and flotation. On the other hand, at higher A/S ratios, solids removal was mostly due to flotation. Thus SS removal in DAF depends on initial SS concentration, particle size and degree of flocculation, etc. Manjunath et al. (2000) evaluated the performance of the laboratory-scale DAF unit to treat wastewater from a slaughterhouse. They found that at a higher A/S ratio of 0.09, SS removal efficiency was nearly 55%, and oils and fat removal efficiency of about 80%. The study also concluded that the DAF unit reduces the strength of wastewater by about 50% and thus fewer loads on the downstream biological treatment unit.

The literature survey also indicated that the current practice is to treat the wastewater from all the slaughtering processes/operations in a combined manner. The most common primary treatment route to treat slaughterhouse wastewater as reported by European Commission (2005), CPCB (2017), IPPC (2003), USEPA (2004), Salminen (2002), USEPA (2002), Gauteng Provincial Government South Africa (2009), EPA Ireland (2008), Enterprise Ireland (2009) and Environment Agency (2009) is presented in Figure 1. It consists of screens, followed by DAF.

Figure 1

Typical primary wastewater treatment route in a slaughterhouse.

Figure 1

Typical primary wastewater treatment route in a slaughterhouse.

Close modal

The wastewater from the lairage and paunch section exerts a significant SS and COD load (Tritt & Schuchardt 1992; Cumby et al. 1999; Mittal 2004). The wastewater from the sticking point has the highest organic strength (Tritt & Schuchardt 1992). Slaughtering operations/processes such as rendering, fleshing, and intestine and tripe washing add FOG and floating solids to the wastewater (Ross et al. 2000; Black et al. 2013). The FOG presence in wastewater may hinder the performance of screening units due to the accumulation of an oily layer on the sieve openings. The continuous deposition may cause choking of screening equipment after a certain period and necessitate periodic cleaning. At the same time, the screened materials contain dung and meat/flesh/fat pieces that may limit their application in the agricultural fields. The effluent from the screens is usually retained in a holding tank before feeding it into the DAF unit. It was observed that if the effluent is held for a longer period of time, the SS in the effluent tends to travel upwards and forms a thick layer of solids at the top surface of the holding tank.

Moreover, the presence of SS even after screening may offset the performance of DAF units due to an increase in SS load. The wastewater from the lairage and paunch section, which principally contains SS when fed to DAF, also increases the hydraulic load on DAF. Hence, it is necessary to rethink and revisit the primary wastewater treatment in the slaughterhouse industry. The authors feel that the segregation of wastewater from the individual slaughtering process/operation based on the nature of similarity may offer additional benefits such as pollutant specific target treatment, distributed hydraulic load and recovery of useful products for reuse. Therefore, the main objective of this study is to:

  • Segregate the wastewater streams from the individual slaughtering process/operations based on the nature of similarity.

  • Design, implement and evaluate the performance of an improved primary wastewater treatment system for a slaughterhouse.

The improved primary treatment system in this study is the result of a detailed literature review, physico-chemical characterization of wastewater emanating from the individual slaughterhouse processes/operation, water consumption patterns and close observations.

Study area and approach

This study was carried out in a slaughterhouse with a slaughtering capacity of 1,000 buffaloes per day and is located in Uttar Pradesh, India. The slaughterhouse follows International Standards and is Hazard Analysis Critical Control Point, ISO 22000:2005, and ISO 9001:2015 certified. The starting point for developing an improved primary treatment was the implementation of segregation of streams; hence a detailed plan was worked out to segregate the various wastewater streams depending on their similar nature, and taking into account the existing wastewater conveyance network, topography and ease of execution. Figure 2 presents the implementation plan for the segregation of streams in the slaughterhouse industry. Dung containing streams from lairage and paunch room were segregated, and FOG containing streams from fleshing, intestine and tripe washing and rendering were separated to facilitate specific treatment and removal of targeted pollutants. Similarly, the bloodstream from the slaughtering area and salt-containing stream from the hide storage area were also separated to prevent its entry into the ETP. This article specifically deals with the wastewater from the lairage and paunch section, rendering, intestine and tripe washing, fleshing and the carcass hall for treatment, removal and recovery of SS and FOG.

Figure 2

Various slaughtering processes/operations and their segregation.

Figure 2

Various slaughtering processes/operations and their segregation.

Close modal

The improved primary wastewater treatment system

The wastewater from the lairage section was treated independently with inclined 500 μm parabolic screens referred to as a hydrasieve. The filtrate from the hydrasieve was then mixed with the paunch room wastewater, and the resulting mixture of streams was treated with a 200 μm externally fed rotary drum filter (EFRDF). The filtrate from the EFRDF was then taken to the primary clarifier after adding alum as a coagulant to remove SS completely. The effluents from the lairage and paunch section were kept separate because the dung particles from the lairage section are completely digested and were used by local farmers as manure in their fields, whereas the dung particles from the paunch section are partially digested.

Using separate screening equipment in the form of 500 μm hydrasieve and 200 μm drum filter for lairage and paunch sections, respectively, substantially reduced SS loads, improved the performance of the treatment units and increased the overall life of the equipment. The FOG containing streams from rendering, fleshing, and intestine and tripe washing contains floating solids. Thus, the FOG containing streams were first routed through the skimming tank, wherein floating solids are recovered from the top.

The effluent from the skimming tank was then fed to the DAF unit. It is important to mention here that using a skimming tank before the DAF removes a substantial fraction of FOG and prevents the floating solids from forming a thick layer at the top surface of the feed/holding tank. This top layer subsequently starts degrading, creates unaesthetic conditions due to foul odour, and it becomes difficult to remove the thick layer of floating solids periodically. Moreover, removing floating solids in a skimming tank reduces the significant load of floating solids, which may upset DAF performance. The workings of the hydrasieve, EFRDF, skimming tank and DAF is explained in the following sections.

Hydrasieve

A hydrasieve is a curved concave type of stationary screen. Wastewater is pumped to the overflow trough located at the top of the hydrasieve screen. As the wastewater slides on the screen's surface, the solid materials are trapped in the screen. Separated particles move down to the bottom and fall in a hopper due to the effect of subsequent flow impulsive force, the angular orientation of the screen and the weight of solids. These screens can be manufactured either in perforations or in a mesh pattern. The screen wires, referred to as wedge wire, are triangular in cross-section, which helps liquids to attach hydraulically to the bars, leaving any solids on the upward portion of the screen plate (Ross et al. 1980; USEPA 2002). The hydrasieve offers advantages including low power requirement, ease of operation, minimum moving parts and there is no operator contact with the liquid during the cleaning operation.

Externally fed rotary drum filter

An EFRDF has a screening or straining medium which is mounted on a cylinder that rotates at a fixed rotation per minute (rpm). The wastewater flows into the top of the unit and passes through the interior, with solids collected on the exterior. Drum screens are mostly fabricated either in mesh or wedge wire only, and perforations drum screens are quite uncommon. To prevent clogging, the screen is sprayed continuously with water using nozzles. These types of screens are least susceptible to clogging caused by solids (Ross et al. 1980; USEPA 2002).

Skimming tank

Skimming tanks are generally installed as a pre-treatment unit to remove floating substances like oils, fats, waxes, free fatty acids, soaps and floating debris (Rao 2005). A skimming tank is a chamber arranged such that floating matter rises and remains on the surface of wastewater until removed manually or mechanically. The effluent free of FOG is collected continuously through an outlet located at a certain depth with curtain walls and a deep scum board (Punmia & Jain 2005). Floating matters are removed either manually or with the help of mechanical equipment.

Dissolved air flotation

Flotation is a very effective method of separating solids and liquid to remove low-density particles that tend to float. Air flotation is used to thicken the solids, and separation of solids is achieved by introducing fine air bubbles. The DAF has four major components: compressor, high-pressure pump, saturator and flotation chamber. The pressurized air is brought in contact with the recycled wastewater in a saturator, and sufficient time is given to allow the air to dissolve in wastewater. The mixture of air and wastewater is introduced in the main chamber. Due to the sudden release in pressure, microbubbles are formed that attach themselves to particles and travel upwards to form a floating layer (Srinivasan & Viraraghavan 2009).

After segregating the streams based on their nature of similarity and implementing improved primary treatment systems as described above, individual streams were studied for the quantitative and qualitative assessment, which are addressed later.

Secondary biological treatment system

Substantial removal of SS and FOG was achieved after successful implementation of an improved primary treatment system, which ensured the reduction in organic load on downstream secondary treatment system. Accordingly, the effluent was further treated a UASB reactor followed by an activated sludge process (ASP). The performance of the secondary treatment system was assessed by collecting integrated samples for 10 h at the inlet and outlet of the UASB reactor and ASP-secondary clarifier system. All the samples were analyzed for SS, COD, BOD, total Kjeldahl nitrogen (TKN) and total phosphate (TP) in compliance with the procedures in the Standard Methods for the examination of water and wastewater, American Public Health Association (APHA), 2005. The results presented on the performance evaluation of the secondary biological treatment system are representative of three sampling events after the successful implementation and commissioning of the improved primary treatment system. Other operating parameters such as food to microorganism ratio, hydraulic retention time (HRT), solids retention time (SRT), mixed liquor suspended solids (MLSS), oxygen uptake rate, specific oxygen uptake rate and sludge volume index for ASP were calculated according to Metcalf & Eddy (2003) and Qasim (1998).

An improved primary wastewater treatment system was designed and installed on a full scale. The improved primary treatment system was studied for a period of one year for its effectiveness, operational difficulties, ease and efficacy. The quantitative and qualitative assessments of SS and FOG streams after segregation are shown in Table 2. Figure 3 shows pictures of segregated blood, dung and FOG streams from various slaughtering operations.

Table 2

Details of effluent generation, concentrations of major pollutants after segregation (capacity 1,000 buffaloes/day)

Stream(s)Flow (m3/d)ConcentrationTarget parameters
Lairage 75–90 SS: 0.6–1.5% SS, COD 
Paunch 200–250 SS: 1.0–2.5% SS, COD 
Hide fleshing, intestine and tripe washing, rendering 250–300 FOG: 1.2–3.5% FOG 
Blood 80–90 COD: 31,600–121,600 mg/L COD, BOD 
Salts 8–10 TDS: 20.0–22.0% TDS 
Stream(s)Flow (m3/d)ConcentrationTarget parameters
Lairage 75–90 SS: 0.6–1.5% SS, COD 
Paunch 200–250 SS: 1.0–2.5% SS, COD 
Hide fleshing, intestine and tripe washing, rendering 250–300 FOG: 1.2–3.5% FOG 
Blood 80–90 COD: 31,600–121,600 mg/L COD, BOD 
Salts 8–10 TDS: 20.0–22.0% TDS 
Figure 3

Photograph of wastewater streams after segregation in a slaughterhouse.

Figure 3

Photograph of wastewater streams after segregation in a slaughterhouse.

Close modal

The segregated bloodstream (86 L/buffalo, COD 31,600–121,600 mg/L) was sent to the decanter centrifuge for blood meal production, thereby preventing the significant organic load from entering the ETP. The average daily quantity of blood meal produced was 1.5 tonnes per day (T/day) with 90% protein and 4% moisture content. The salt stream from the hide storage section (∼5 L/buffalo, TDS 25–32%) was also separated for salt recovery. There is the potential to recover salts to the tune of 2.5–3 T/day. Intestinal contents, which are partially digested, are also a major pollutant in slaughterhouses (Carawan & Pilkington 1986). The wet weight of a paunch material ranges between 22 and 31 kg per cattle (Carawan et al. 1979). The paunch is cut with the help of a knife, and wet paunch material is taken out manually, and any excess solids stuck on the inner wall of the paunch are rinsed with water, which generates wastewater. In a slaughterhouse, the average water consumption per buffalo was 1,114 L, and the corresponding wastewater generation was 916–1,089 L (Shende et al. 2021).

Efficacy of an improved primary wastewater treatment system

The schematic and performance of an improved primary treatment system are shown in Figure 4 and the results presented are the average of five sampling events taken during 2019. The samples were taken at the end of each hour during the operation of the individual solid–liquid separation equipment and mixed to form the representative sample for analysis.

Figure 4

Schematic diagram of Improved Primary Treatment System for Slaughterhouse Wastewater and its performance.

Figure 4

Schematic diagram of Improved Primary Treatment System for Slaughterhouse Wastewater and its performance.

Close modal

The average wastewater generation from the lairage section varies between 75 and 90 m3/d, and the SS removal efficiency from the hydrasieve was around 75% at an HLR of 6.25 m3/m2/h. Usually, HLR for hydrasieves varies between 2.4 and 72 m3/m2/h (Metcalf & Eddy 2003). The SS removal efficiency using a hydrasieve in this study was higher than that reported by Wright (2018). This may be attributed to the opening size used for the hydrasieve screens. Wright (2018) used a hydrasieve with an opening of 2.5 mm rather than 500 μm, as in this study. It is important to maintain harmony between screen size and HLR because the reduction in screen opening reduces applicable HLR. The same was also observed in this study, where an increase in HLR beyond 6.25 m3/m2/h resulted in the splashing of water over the screen surface and a reduction in SS removal efficiency.

Nevertheless, the hydrasieve with a screen opening of 500 μm worked satisfactorily at an HLR of 6.25 m3/m2/h with steady SS removal efficiency. The wastewater from the paunch section, carcass hall, meat packaging and refrigeration was mixed with the filtrate obtained from the hydrasieve. The resultant mixture had a flow rate in the range of 525–610 m3/d and was then fed to the drum filter at an HLR of 10 m3/m2/h, which achieved 55% average SS removal efficiency. The outlet of the drum filter had 1,544 ± 330 mg/L of SS and 1,804 ± 168 mg/L of COD concentrations. It was observed that the SS at the outlet of the drum filter was mostly colloidal. These colloidal solids were removed using coagulation with an alum dose of 250–300 mg/L. After coagulation and subsequent settling in the primary clarifier, SS and COD removal efficiencies of nearly 86% and 52% were achieved, respectively. The results obtained in this study were comparable with the studies done by Núñez et al. (1999) and Aguilar et al. (2005) to treat slaughterhouse wastewater using coagulation with alum. The sludge volume in this study was found to be 150 ± 30 mL/L, which was higher than the reported value of 85 mL/L while treating slaughterhouse wastewater by Satyanarayan et al. (2005). This is because the initial SS concentration in the study carried out by Satyanarayan et al. (2005) was only 310 mg/L rather than 1,560 ± 350 mg/L in the present study. The effluent obtained at the outlet of the primary clarifier was found to have very low organic strength with COD and BOD concentrations of 850 ± 125 and 596 ± 90 mg/L, respectively. The sludge from the primary clarifier was dewatered using a filter press. The average moisture content of the dewatered sludge was 65% and the remaining dry solids (DS) was 35%. The dewatered solids from the filter press are around 3,000 kg/day.

The separated solids from the hydrasieve, EFRDF and filter press were 6,000, 12,000, and 3,000 kg/day, respectively. The average moisture content (MC) of the separated solids from the hydrasieve and EFRDF was 85%, and for the filter press was 65%. The separated solids were dewatered, dried and manufactured into briquettes with a gross calorific value of 3,032 Kcal/kg.

The skimming tank was efficient in removing FOG, meat/flesh and fat pieces. The SS concentrations at the inlet of the skimming tank had a wide variation with concentrations of 6,044 ± 2,985 mg/L. However, the SS concentration at the outlet of the skimming tank outlet was relatively low at 1,328 ± 455 mg/L, resulting in nearly 75% removal efficiency. As far as the removal of FOG is concerned, the skimming tank achieved more than 90% removal efficiency. The outlet of the skimming tank was then fed to the DAF unit.

The A/S ratio in the DAF in this study was more than the values reported by Ross et al. (2000) and Nardi et al. (2008). This is mainly because of the air injection rate and the recycle pressure, which was maintained at 3–3.5 m3/h and 6.5 kg/cm2, respectively. The SS removal efficiency in the present study is comparable to the values reported by Nardi et al. (2008). However, the FOG removal efficiency in the present study was comparatively lower than the values reported by Ross et al. (2000) and Nardi et al. (2008). After the DAF unit, the effluent obtained had FOG concentrations in the range of 80–100 mg/L. The operating parameters and the comparative assessment of the performance of the DAF unit are shown in Table 3.

Table 3

Operating parameters and comparative assessment of the performance of DAF unit

Operating parametersFOG streams from fleshing, rendering, and intestine and tripe washing at the outlet of the skimming tank (present study)Wastewater from poultry rendering facility (Ross et al. 2000)Wastewater from poultry slaughterhouse (Nardi et al. 2008)
Total flow (m3/h) 68 74.95 105.43 
Recycle rate (m3/h) 22.44 20.44 42.18 
Percentage recycling ratio (%) 33 27.27 40 
Recycle pressure (kg/cm26.5 5.6 4.5 
Air injection rate (m3/h) 3–3.5 1.84 – 
Surface area (m211.93 16.72 32 
HLR (feed only) (m3/m2/h) 3.82 4.48 2.4 ± 0.2 
HLR (including recycle) (m3/m2/h) 5.69 5.70 4.61 
Solid loading rate (kg/m2/h) 4.98–10.16 195.69 0.916 ± 0.20 
Air to solid ratio (mL/mg) 0.016 0.0006 0.030 ± 0.008 
Influent SS mg/L 1,328 ± 455 43,706 861 ± 204 
Influent FOG mg/L 2,382 ± 488 18,568 182 ± 29 
Effluent SS mg/L 214 ± 29 262 224 ± 53 
Effluent FOG mg/L 80–100 72 <2 
Operating parametersFOG streams from fleshing, rendering, and intestine and tripe washing at the outlet of the skimming tank (present study)Wastewater from poultry rendering facility (Ross et al. 2000)Wastewater from poultry slaughterhouse (Nardi et al. 2008)
Total flow (m3/h) 68 74.95 105.43 
Recycle rate (m3/h) 22.44 20.44 42.18 
Percentage recycling ratio (%) 33 27.27 40 
Recycle pressure (kg/cm26.5 5.6 4.5 
Air injection rate (m3/h) 3–3.5 1.84 – 
Surface area (m211.93 16.72 32 
HLR (feed only) (m3/m2/h) 3.82 4.48 2.4 ± 0.2 
HLR (including recycle) (m3/m2/h) 5.69 5.70 4.61 
Solid loading rate (kg/m2/h) 4.98–10.16 195.69 0.916 ± 0.20 
Air to solid ratio (mL/mg) 0.016 0.0006 0.030 ± 0.008 
Influent SS mg/L 1,328 ± 455 43,706 861 ± 204 
Influent FOG mg/L 2,382 ± 488 18,568 182 ± 29 
Effluent SS mg/L 214 ± 29 262 224 ± 53 
Effluent FOG mg/L 80–100 72 <2 

The effluents obtained from the DAF unit and primary clarifier were mixed in the equalization tank. The resultant wastewater was found to have COD and BOD concentrations of 849 ± 125 and 610 ± 53 mg/L, and SS and FOG concentrations of less than 200 and 100 mg/L, respectively.

The summary of SS removed through the multi-intervention approach consisting of the hydrasieve, EFRDF, skimming tank and DAF along with the quantities of valuable resources from blood and salt stream is presented in Table 4. It is evident from Table 4 that the hydrasieve and EFRDF separated significant SS from the effluent. Moreover, a simple intervention like a skimming tank proved very efficient and removed FOG significantly (4–4.5 kg/buffalo).

Table 4

Summary of solids and FOG recovered in treatment units

Treatment unitSS separated/DS/FOG removed
Hydrasieve SS: 6 kg/buffalo (digested, MC: ∼85–87%), DS: 0.9–1 kg/buffalo 
EFRDF SS: 12 kg/buffalo (partially digested, MC: ∼85–87%), DS: 1.8–2 kg/buffalo 
Primary clarifier → filter press SS: 2–3 kg/buffalo (MC: ∼60–65), DS: 0.8–1 kg/buffalo 
SS recovered from lairage and a paunch section either by dry scrapping or by manually emptying the paunch SS: 10–13 kg/buffalo (MC: ∼85%), DS: 1.5–2 kg/buffalo 
Skimming tank SS: 1.1–1.4 kg/buffalo FOG: 4–4.5 kg/buffalo 
DAF SS: ∼0.3 kg/buffalo FOG: 0.5–0.6 kg/buffalo 
Separated bloodstream COD: 31,600–121,600 mg/L, daily blood meal production 1.5 T/day with protein content of ∼ 90% 
Separated salt stream Potential salt recovery: ∼ 2,000–2,200 kg/day 
Treatment unitSS separated/DS/FOG removed
Hydrasieve SS: 6 kg/buffalo (digested, MC: ∼85–87%), DS: 0.9–1 kg/buffalo 
EFRDF SS: 12 kg/buffalo (partially digested, MC: ∼85–87%), DS: 1.8–2 kg/buffalo 
Primary clarifier → filter press SS: 2–3 kg/buffalo (MC: ∼60–65), DS: 0.8–1 kg/buffalo 
SS recovered from lairage and a paunch section either by dry scrapping or by manually emptying the paunch SS: 10–13 kg/buffalo (MC: ∼85%), DS: 1.5–2 kg/buffalo 
Skimming tank SS: 1.1–1.4 kg/buffalo FOG: 4–4.5 kg/buffalo 
DAF SS: ∼0.3 kg/buffalo FOG: 0.5–0.6 kg/buffalo 
Separated bloodstream COD: 31,600–121,600 mg/L, daily blood meal production 1.5 T/day with protein content of ∼ 90% 
Separated salt stream Potential salt recovery: ∼ 2,000–2,200 kg/day 

Secondary biological treatment

The secondary biological treatment system and its performance is presented in Figure 5. During the study period, it was found that the concentrations of SS, COD, BOD, TKN and TP of the primary treated wastewater were 187 ± 20, 823 ± 186, 540 ± 104, 66 ± 18, and 5.3 ± 0.69 mg/L, respectively. The same wastewater was fed to full-scale UASB reactors at an average organic loading rate (OLR) of 1.54 ± 0.34 kg COD·m3/d with an HRT of 12.8 h at an upflow velocity Vup of 0.15 m/h. The average COD and BOD removal efficiencies after the UASB were 33% and 37%, respectively, which are less than the reported values by Sayed et al. (1987). They operated the laboratory-scale UASB at OLR 2.5–4.0 kg COD·m3/d with an HRT of 9 h and achieved 56% COD removal efficiency while treating slaughterhouse wastewater with an initial COD concentration of 1,086 mg/L. The difference in the results can be attributed to the huge difference in the scale of operation. In the present case, UASB was able to reduce the organic load to aerobic biological treatment systems by at least 35%. No biomass washout was observed during the reactor operation. The outlet from the UASB was fed to the ASP, which was operated at an SRT of 8 days and HRT of 7.5 h. The recycle ratio of return sludge to the influent was maintained at 0.6. The ASP performed satisfactorily with the average COD removal efficiency of 68%. The average BOD removal efficiency of the ASP was 92%, proving that the ASP was effective in bringing down the BOD of treated effluent to meet the effluent discharge norms to ≤30 mg/L. The MLSS to mixed liquor volatile suspended solids ratio was 0.7, and the oxygen uptake rate was 30 mg O2/L·h indicating the presence of healthy biomass. The sludge volume index was found to be between 89 and 94 mL/g showing good settling of MLSS. This is also evident from the solids concentration of the return activated sludge, which varied between 8,570 and 9,250 mg/L. The TKN and TP values after ASP were also found to be meeting the effluent discharge standards.

Figure 5

Performance evaluation of secondary biological treatment system.

Figure 5

Performance evaluation of secondary biological treatment system.

Close modal

As per the revised effluent discharge standards for slaughterhouse industries (Environmental Protection Rules, 1986), SS needs to be brought down to less than 50 mg/L. However, the SS concentration in the ASP outlet was 85 ± 8 mg/L, which is higher than the regulatory standards. However, the slaughterhouse industry operates a tertiary treatment system consisting of pressure sand filter followed by activated carbon filter and/or polishing ponds which can take care of the SS. The combined performance of the UASB followed by the ASP was satisfactory, and the treated effluent at the outlet of the ASP met the effluent discharge standards in terms of COD, BOD, TKN and TP. The SS concentration was further reduced with the help of a tertiary treatment system consisting of a pressure sand filter and an activated carbon filter.

One of the major challenges in dealing with slaughterhouse industrial wastewater is the effective primary treatment system for removing SS and FOG, which is a major hurdle in downstream treatment. Conventionally, wastewater generated from various slaughtering operations is treated in a combined manner. The segregation of streams based on the nature of similarity and target-specific pollutant treatment was proven to be very effective in managing slaughterhouse wastewater. Using simple solid–liquid separation equipment such as a hydrasieve (500 μm) and EFRDF (200 μm) with suitable screen sizes proved was effective compared to sophisticated equipment such as centrifuge, screw press, vibratory screens, etc. The intervention of the skimming tank before DAF was found to reduce considerable SS and FOG load on the DAF. The effluent obtained After using the improved primary wastewater treatment system, the effluent obtained had SS and FOG less than 200 mg/L and 100 mg/L, respectively. The primary treated effluent was managed with a UASB reactor followed by a conventional ASP. The secondary biological treatment system performed smoothly without experiencing operational difficulties and achieved effluent discharge standards in terms of COD, BOD, TKN and TP. Segregation of similar streams and making provisions for removing dung solids SS and FOG through multi-intervention approach offered benefits in relation to resource recovery, distributed hydraulic load reduced waste load, and ease in wastewater treatment. Thus, the segregation of streams from the individual slaughterhouse processes/operation based on its nature of similarity and separate treatment is key to effectively managing wastewater in the slaughterhouse industry.

The help by M/s FEPL, Rampur (Uttar Pradesh), and Barabanki (Uttar Pradesh) is gratefully acknowledged.

The authors declare no conflict of interest.

All relevant data are included in the paper or its Supplementary Information.

Aguilar
M. I.
,
Sáez
J.
,
Lloréns
M.
,
Soler
A.
,
Ortuño
J. F.
,
Meseguer
V.
&
Fuentes
A.
2005
Improvement of coagulation-flocculation process using anionic polyacrylamide as coagulant aid
.
Chemosphere
58
,
47
56
.
https://doi.org/10.1016/j.chemosphere.2004.09.008
.
American Public Health Association (APHA)
2005
Standard Methods for the Examination of Water and Wastewater
, 21st edn.
APHA
,
Washington, DC
.
Black
M.
,
Canova
M.
,
Rydin
S.
,
Scalet
B. M.
,
Roudier
S.
&
Sancho
L. D.
2013
Best available techniques (BAT) reference document on for the tanning of hides and skin
.
European Commission
.
http://dx.doi.org/10.2788/13548
.
Carawan
R. E.
&
Pilkington
D. H.
1986
Reduction in Waste Load from a Meat Processing Plant-Beef
.
North Carolina Agricultural extension service
,
Raleigh, North Carolina
.
Carawan
R. E.
,
Chambers
J. V.
&
Zall
R. R.
1979
Meat Processing Water and Wastewater Management
.
North Carolina Agricultural Extension Service
,
Raleigh, North Carolina
.
Central Pollution Control Board (CPCB)
2017
Revised Comprehensive Industry Document on Slaughterhouses
. Government of India.
Cumby
T. R.
,
Brewer
A. J.
&
Dimmock
S. J.
1999
Dirty water from dairy farms, I: biochemical characteristics
.
Bioresource Technology
67
,
155
160
.
https://doi.org/10.1016/S0960-8524(98)00104-7
.
Department of Agriculture and Rural Development
2009
Guideline Manual for the Management of Abattoirs and Other Waste of Animal Origin
. Gauteng Provincial Government, South Africa.
Enterprise Ireland
2009
Sustainable Practices in Irish Beef Processing
.
Enterprise Ireland, Dublin
.
Environment Agency
2009
How to Comply with Your Environmental Permit. Additional Guidance for The Red Meat Processing (Cattle, Sheep and Pigs) Sector (EPR 6.12)
.
Environment Agency, Bristol
.
Environmental Protection Agency
2008
BAT Guidance Note on Best Available Techniques for the Slaughtering Sector
, 1st edn.
Environmental Protection Agency
,
Wexford, Ireland
.
Environmental Protection Rules, Government of India
1986
Standards for discharge of effluents from slaughterhouse, meat processing units and seafood industry. Notified on 28.10.2016
.
European Integrated Pollution Prevention and Control (IPPC) Bureau
2003
Reference Document on Best Available Techniques in Common Waste Water and Waste Gas Treatment/Management Systems in the Chemical Sector, 472
.
European Commission
2005
Reference Document on Best Available Techniques in the Slaughterhouses and Animal by-Products Industries
.
Brussels
.
Fernandes
L.
,
Mckyes
E.
&
Obidniak
L.
1988
Performance of a continuous belt microscreening unit for solid liquid separation of swine waste
.
151
155
.
Fleming
R.
&
Macalpine
M.
2003
Evaluation of Mechanical Liquid/Solid Manure Separators
.
Prepared for Ontario Pork, Project No. 02/39. Ridgetown College and University of Guelph, Ridgetown and Ontario
.
Gilkinson
S.
&
Frost
P.
2007
Evaluation of Mechanical Separation of Pig and Cattle Slurries by a Decanting Centrifuge and a Brushed Screen Separator
. Agri-Food and Biosciences Institute, Hillsborough, Northern Ireland, pp.
1
47
.
Giorgia
C.
2013
PhD. Thesis: Assessment of Different Solid-Liquid Separation Techniques for Livestock Slurry
.
University DEGLI Studi DI Milano
.
Gooch
C. A.
,
Inglis
S. F.
&
Czymmek
K. J.
2005
Mechanical solid-liquid manure separation: Performance evaluation on four New York State dairy farms – a preliminary report
. In
ASAE Annual International Meeting
. p.
0300
.
https://doi.org/10.13031/2013.19506
Kitchener
J. A.
&
Gochin
R. J.
1981
The mechanism of dissolved air flotation for potable water: basic analysis and a proposal
.
Water Research
15
,
585
590
.
https://doi.org/10.1016/0043-1354(81)90021-X
.
Lovett
D. A.
&
Travers
S. M.
1986
Dissolved air flotation for abattoir wastewater
.
Water Research
20
,
421
426
.
https://doi.org/10.1016/0043-1354(86)90188-0
.
Manjunath
N. T.
,
Mehrotra
I.
&
Mathur
R. P.
2000
Treatment of wastewater from slaughterhouse by DAF-UASB system
.
Water Research
34
,
1930
1936
.
https://doi.org/10.1016/S0043-1354(99)00337-1
.
Metcalf & Eddy
2003
Wastewater Engineering
, 4th edn.
Tata McGraw-Hill Publishing Company Limited
,
New Delhi, India
.
Miranda
L. A. S.
,
Henriques
J. A. P.
&
Monteggia
L. O. A.
2005
Full-scale UASB reactor for treatment of pig and cattle slaughterhouse wastewater with a high oil and grease content
.
Brazilian Journal of Chemical Engineering
22
,
601
610
.
https://doi.org/10.1590/S0104-66322005000400013
.
Mittal
G. S.
2004
Characterization of the effluent wastewater from abattoirs for land application
.
Food Reviews International
20
,
229
256
.
https://doi.org/10.1081/FRI-200029422
.
Møller
H. B.
,
Sommer
S. G.
&
Ahring
B. K.
2002
Separation efficiency and particle size distribution in relation to manure type and storage conditions
.
Bioresource Technology
85
,
189
196
.
https://doi.org/10.1016/S0960-8524(02)00047-0
.
Nardi
I. R.
,
Fuzi
T. P.
&
Nery
V. D.
2008
Performance evaluation and operating strategies of dissolved-air flotation system treating poultry slaughterhouse wastewater
.
Resource Conservation and Recycling
52
,
533
544
.
https://doi.org/10.1016/j.resconrec.2007.06.005
.
Núñez
L. A.
,
Fuente
E.
,
Martínez
B.
&
García
P. A.
1999
Slaughterhouse wastewater treatment using ferric and aluminium salts and organic polyelectrolites
.
Journal of Environmental Science & Health – Part A
34
,
721
736
.
https://doi.org/10.1080/10934529909376861
.
Punmia
B. C.
&
Jain
A. K.
2005
Wastewater Engineering
.
Laxmi Publications Private Limited, New Delhi, India
.
Qasim
S. R.
1998
Wastewater Treatment Plants – Planning, Design and Operation
, second ed.
Technomic Publishing Company
,
Lancaster, Pennsylvania
.
Rao
P. V.
2005
Textbook of Environmental Engineering
.
Prentice-Hall of India Private Limited
,
New Delhi
.
Ross
S. A.
,
Guo
P. H. M.
&
Jank
B. E.
1980
Design and Selection of Small Wastewater Treatment System. Environment Protection Service Report Series. Environment Canada
Ottawa, Canada.
Ross
C. C.
,
Smith
B. M.
&
Valentine
G. E.
2000
Rethinking Dissolved Air Flotation (DAF) design for industrial pre-treatment
. In
WEF and Purdue University Industrial Wastes Technical Conference
, St Louis, Missouri, 21-24 May.
Salehion
A. R.
,
Minaei
S.
&
Razavi
S. J.
2013
Design and performance evaluation of a screw press separator for separating dairy cattle manure
.
International Journal of Agronomy and Plant Production
4
,
3849
3858
.
Salminen
E.
2002
Finnish Expert Report on Best Available Techniques in Slaughterhouses and Installations for the Disposal or Recycling of Animal Carcasses and Animal Waste. The Finnish Environment, 539
.
Finnish Environment Institute
,
Helsinki
,
Finland
.
Satyanarayan
S.
,
Ramakant
&
Vanerkar
P.
2005
Conventional approach for abattoir wastewater treatment
.
Environmental Technology
26
,
441
447
.
https://doi.org/10.1080/09593332608618554
.
Sayed
S. K. I.
,
Van Campen
L.
&
Lettinga
G.
1987
Anaerobic treatment of slaughterhouse waste using a granular sludge UASB reactor
.
Biological Wastes
21
(
1
),
11
28
.
Shende
A. D.
,
Dhenkula
S.
,
Waghambare
A.
,
Rao
N. N.
&
Pophali
G. R.
2021
Water consumption, wastewater generation and characterization of a slaughterhouse for resource conservation and recovery
.
Water Practise & Technology
.
https://doi.org/10.2166/wpt.2021.122
.
Srinivasan
A.
&
Viraraghavan
T.
2009
Dissolved air flotation in industrial wastewater treatment
. In:
Water and Wastewater Treatment
,
(edited by Vigneswaran S.)
.
Encyclopedia of Life Support Systems (EOLSS) Publisher
,
Oxford, UK
.
Sunder
G. C.
&
Satyanarayan
S.
2013
Efficient treatment of slaughter house wastewater by anaerobic hybrid reactor packed with special floating media
.
International Journal of Chemical and Physical Science
2
,
73
81
.
Tritt
W. P.
&
Schuchardt
F.
1992
Materials flow and possibilities of treating liquid and solid wastes from slaughterhouses in Germany. A review
.
Bioresource Technology
41
,
235
245
.
https://doi.org/10.1016/0960-8524(92)90008-L
.
United States Environmental Protection Agency (USEPA)
2002
Development Document for the Proposed Effluent Limitations Guidelines and Standards for the Meat and Poultry Products Industry Point Source Category.
Washington DC.
United States Environmental Protection Agency (USEPA)
2004
Effluent Limitations Guidelines and New Source Performance Standards for the Meat and Poultry Products Point Source Category, 69, (173)
. Washington DC.
Wright
W. F.
2018
Dairy Manure Particle Size Distribution, Properties, and Implications for Manure Handling and Treatment. The Society for Engineering in Agricultural, Food and Biological System, Paper No. 054105
.
https://doi.org/10.13031/2013.19507
.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY-NC-ND 4.0), which permits copying and redistribution for non-commercial purposes with no derivatives, provided the original work is properly cited (http://creativecommons.org/licenses/by-nc-nd/4.0/).