The aim of the present study was to investigate the efficiency of integrated up-flow anaerobic sludge blanket (UASB) as anaerobic system followed by membrane bioreactor (MBR) as aerobic system for the treatment of greywater for unrestricted reuse. Pilot-scale UASB and MBR units were installed and operated in the NRC, Egypt. Real raw greywater was subjected to UASB and the effluent was further treated with microfiltration MBR. The necessary trans-membrane pressure difference is applied by the water head above the membrane (gravity flow) without any energy input. The average characteristics of the raw greywater were 95, 392, 298, 10.45, 0.4, 118.5 and 28 mg/L for total suspended solids (TSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total phosphates, nitrates, oil and grease, and total Kjeldahl nitrogen (TKN), respectively. The pH was 6.71. The UASB treatment efficiency reached 19.3, 57.8, 67.5 and 83.7% for TSS, COD, BOD5 and oil and grease, respectively. When the UASB effluent was further treated with MBR, the overall removal rate achieved 97.7, 97.8, 97.4 and 95.8% for the same parameters successively. The characteristics of the final effluent reached 2.5, 8.5, 6.1, 0.95, 4.6 and 2.3 mg/L for TSS, COD, BOD, phosphates, oil and grease and TKN, respectively. This final treated effluent could cope with the unrestricted water reuse of local Egyptian guidelines.

INTRODUCTION

Most wastewater produced in the Middle East and North African (MENA) countries is inefficiently treated due to poor maintenance of the equipment, high electricity cost and lack of recent technologies (Jefferson et al. 2000). In Egypt, the reuse of inefficiently treated wastewater or even directly without treatment for irrigation purposes is serving as a carrier for diseases or causing water pollution when discharged to water bodies (Abdel-Shafy & Aly 2007). In the last decade, several water treatment technologies have been used in the MENA region, but with little success in relation to pathogen removal (Regelsberger et al. 2007; Abdel-Shafy & Aly 2007). This significantly reduces the opportunity of using the treated effluent for unrestricted irrigation for crops of higher value (Abdel-Shafy & Abdel-Sabour 2006).

Conversely, municipal wastewater separation into black and greywater proved to be an efficient system to prevent the contamination of greywater and reduces the volume of faecal contaminated wastewater as well as reducing the cost of treatment (Regelsberger et al. 2007). Indoor domestic water demand in developed countries usually ranges between 100 and 180 L/d person equivalent (PE) or 36–66 m3/y PE, comprising 30–70% of the total urban water demand (Nolde 2005). In urban areas the most feasible greywater reuse option is for toilet flushing, which can reduce individual in-house net water demand by 40–60 L/d PE. If this practice becomes widespread, reduction of 10–25% in urban water demand can be achieved. It is estimated that in 2023, with a 30% penetration ratio (i.e. 30% of houses having greywater reuse units installed), greywater reuse for toilet flushing in the domestic sector could save about 50 million cubic meters (MCM)/y in Mediterranean countries (Nolde 2005). This consists of about 5% of the projected national urban water demand and is equal to the capacity of a medium-sized seawater desalination plant. In Egypt, greywater treatment and reuse is still in the experimental and research studies (Abdel-Shafy et al. 2014).

Recently, many researchers have studied the greywater treatment by application of different technologies including Rotating Biological Contactor (Nolde 2005) and artificial wetlands (Abdel-Shafy et al. 2013).

The up-flow anaerobic sludge blanket (UASB) proved to be a cost-effective, simple and low energy consumption pre-treatment system for wastewater. In developing countries there is a need for low-cost reliable methods for wastewater treatment without high energy input (Ghangrekar et al. 2002). Subsequently, the UASB system has been mainly used in tropical countries due to its high performance in warm ambience (Abdel-Shafy et al. 2009). Over 200 installations worldwide, the success of the UASB reactor can be attributed to its capability to retain a high concentration of sludge and efficient solids, liquid and water phase separation. Moreover, the removed organic matter is converted into biogas, as a source of energy. In the UASB system all the benefits of anaerobic systems over aerobic treatment are retained, e.g. energy production, low excess sludge production and low volume requirement. Due to the better stability and low production of the sludge under the anaerobic process, the cost involved in further treatment can considerably be reduced (Ghangrekar et al. 2002; Lettinga et al. 1980). Nevertheless, the effluent from UASB does not, generally, comply with the local standards for treated effluent reuse, particularly in arid and semiarid areas (Abdel-Shafy et al. 2009). It is worth mentioning that methane is released from the UASB reactor in low-loading and it depends on the organic strength of the treated wastewater. The average biogas production depends mainly on the level of total chemical oxygen demand (t-COD) and soluble chemical oxygen demand (s-COD) fed to the UASB reactor. Greywater is well known for being relatively within low values of biodegradable organic matter and the nutrient imbalances limits the effectiveness of biological treatment (Al-Jayyousi 2003). Meanwhile, the methane released from the UASB reactor may lead to greenhouse gas emission which is much stronger than that of carbon dioxide. Therefore, the produced gas should be collected and used as a source of energy.

Recently, membrane bioreactor (MBR) technology has gained popularity in wastewater treatment and especially for decentralised and reuse applications (Stephenson et al. 2000; Strathmann et al. 2006; Schier et al. 2009). MBR technology has become a key component in water reclamation schemes due to the possibility to provide high quality of water, e.g. as particle free permeate, removal of microbiological contamination and the cost-effectiveness of reclaimed effluents that are needed to boost water recycling applications in many regions of the world (Daigger et al. 2005; Strathmann et al. 2006). The MBR process was demonstrated to be cost effective over conventional water reclamation systems for urban irrigation (Daigger et al. 2005). Therefore, excellent effluent quality can be obtained and, generally, suitable for reuse, as membranes provide high removal of pathogens including bacteria, protozoa and viruses, resulting in excellent physical disinfection. Moreover, suspended solids and large particles such as colloids are also retained within the bioreactor device. In addition, the organic load is biodegraded, and hence decreased significantly, as indicated by the biochemical oxygen demand (BOD) and COD (Abdel-Shafy & El-Khateeb 2011). It has been documented also that the other pollutant parameters, such as nitrogenous compounds, phosphates and heavy metals, decreased to variable degrees (Abdel-Shafy et al. 2005; Dialynas & Diamadopoulos 2009; Schier et al. 2009).

In this study, integrated anaerobic and aerobic treatment processes for greywater treatment were investigated for its feasibility to replace the existing conventional activated sludge process. The integrated system consisted of a UASB reactor followed by MBR for the treatment of separated real greywater. The characteristics of the treated effluent of each reactor were evaluated according to the permissible level of water reuse suitable for unrestricted irrigation purposes, particularly for the decentralised areas.

MATERIALS AND METHODS

Source of raw greywater

Real municipal wastewater was separated from the origin by piping system into black (B) and greywater (G) and was connected from one house across the Training Demonstration Centre (TDC) site in the National Research Centre, Cairo, Egypt. This house comprises two separated sides. Each side consists of five apartments. The piping system of one side is presently connected to the TDC site as segregated B and G water manholes. The collected greywater (G) is the subject of the present study. It includes wastewater from baths, showers, hand wash basins, washing machines, dishwashers and kitchen sinks.

UASB reactor

Two UASB reactors were erected in the TDC site. The dimensions and operation conditions of the UASB are given in Table 1 according to Abdel-Shafy et al. (2009). The reactors were manufactured from non-transparent polyvinyl chloride (PVC). Greywater was pumped from the manhole sewerage system four times per day to feed the UASB.

Table 1

Dimensions and operating conditions of the up-flow anaerobic sludge blanket for greywater treatmenta

Dimensions and materials 
Volume water 250 L 
Height 3.5 m 
Internal diameter 0.4 m 
Sludge content 22 g/L 
Material of the piping (inlet and outlet) PVC 
Release and retain greywater Valve 
Operating conditions
 
HRT 6 hours 
HLR 1 or 4 m3/m3
OLR 1.103 kg BOD/m3/d 
1.93 kg COD/m3/d 
Dimensions and materials 
Volume water 250 L 
Height 3.5 m 
Internal diameter 0.4 m 
Sludge content 22 g/L 
Material of the piping (inlet and outlet) PVC 
Release and retain greywater Valve 
Operating conditions
 
HRT 6 hours 
HLR 1 or 4 m3/m3
OLR 1.103 kg BOD/m3/d 
1.93 kg COD/m3/d 

OLR = organic loading rate, HRT = the hydraulic residence time (it was calculated according to the equation given by Crites & Tchobanoglous (1998)).

The greywater was introduced at the bottom of the reactor through a pipe with a 50 mm diameter and distributed over the cross-section by means of a perforated Plexiglas plate, which was placed about 40 cm above the feed tube. A tap was placed at the bottom of the reactor to remove the accumulated solids. Four sample ports were placed along the reactor at 1.00 m intervals throughout the height of digestion zone with an additional port at 0.30 m from the top of the reactor. In addition, a port was placed on the reactor at 0.10 m from the bottom (the port used for solids removal). It is necessary to provide suitable habitat for the treatment which is essentially required to obtain a high digestion for greywater. The hydraulic residence time (HRT) of the reactor was allowed to reach steady state. The organic loading rate (OLR) was fixed in the reactor at 1.103 kg BOD/m3/d and 1.93 kg COD/m3/d (Table 1). The performance of the reactor was monitored through 24-hour flow weighted composite samples, taken from inlet and sample ports.

MBR pilot reactor

The MBR unit is especially designed in 2014 that implies a down-scaled version for greywater treatment. It combines the activated sludge process with membrane filtration. Membranes are in the microfiltration range with nominal pore sizes of 0.378 μm guaranteed to provide reliable separation of bacteria and all particulate material. Up-flow aeration from the bottom of the react or is supplied by a compressor of 116 psi (pounds per square inch) pressure capacity meant for all daily aeration, to facilitate aerobic bacterial growth and to minimise any possible fouling or clogging of the membrane unit. In addition, fouling on the surface of the plate and frame module (KUBOTA) is controlled through tangential flow along the membrane surface. The necessary trans-membrane pressure difference is applied by the water head (1.1 m height) above the membrane (gravity flow) without any energy (Strathmann et al. 2006). In this respect, the aeration system of MBR consumes about 60% of the total required energy. A rough estimation of the present study reveals that applying the water head (1.1 m height) for gravity flow of wastewater could save between 30 and 40% of the total required energy. Based on our observation, higher water head up to 1.5–1.7 m should be examined in the near future. The specification of the MBR is given in Table 2.

Table 2

Specification of the pilot membrane bioreactor unit

Item Specification 
Membrane material Polyelectrolyte complex (PEC) 
Membrane surface, m2 0.6 
Number of membranes 
Resistance/pH range 1.5–10 
Resistance/H2O2 (NaOCl), ppm 3,000–5,000 (normal 500) 
Resistance/temperature, °C <50 
Resistance/pressure, mWS Max. 1–3 (1.02 mWS = 10 kPa) 
Item Specification 
Membrane material Polyelectrolyte complex (PEC) 
Membrane surface, m2 0.6 
Number of membranes 
Resistance/pH range 1.5–10 
Resistance/H2O2 (NaOCl), ppm 3,000–5,000 (normal 500) 
Resistance/temperature, °C <50 
Resistance/pressure, mWS Max. 1–3 (1.02 mWS = 10 kPa) 

The small pore sizes of the membrane guarantee retaining nitrifying bacteria and other microorganisms in the reactor. Furthermore, the separation by membranes allows mixed liquor suspended solids concentrations that by far exceed the usual 2–4 g/L in conventional treatment systems. The purpose is to obtain an effluent free of particles and germs. The experiments were carried out in the reactor operated under aerobic conditions (oxygen concentration in the tank: 1–4 mg/L). The continuous aeration provided for MBR limited membrane fouling and maintained the aerobic condition of the reactor.

Schematic operation of the treatment system

The raw greywater was pumped from the manhole to the UASB as anaerobic system. The effluent of the UASB was directed by gravity to the aerobic MBR. The final effluent was reused for unrestricted irrigation. The schematic diagram of the hybrid systems is shown in Figure 1.

Figure 1

Schematic diagram of the treatment system.

Figure 1

Schematic diagram of the treatment system.

Analytical methods

Composite samples of raw greywater and effluents of the two treatment units, namely UASB and MBR, were weekly collected and analysed for the physical and chemical characteristics including pH, total suspended solids (TSS), COD, BOD5, oil and grease, NO3, NO2, ammonia, total phosphates (TP) and total Kjeldahl nitrogen (TKN). The Escherichia coli counts and the count of number of cells or eggs of nematodes (count/L) were carried out in the final effluent samples. These parameters were carried out according to Standard Methods for the Examination of Water and Wastewater (APHA 2005).

RESULTS AND DISCUSSION

Characteristics of raw greywater

The physical and chemical characteristics of the raw greywater were determined on a weekly basis (Table 3). The results indicate that the concentration of total dissolved solids (TDS), TSS, COD, BOD, ammonia-N, TP and oil and grease are within the average levels of medium strength greywater, namely 510, 95, 392, 298.6, 8.4, 10.54 and 118.5 mg/L, respectively. The high concentrations of detergents and the presence of oil and grease in greywater are known to be slowly biodegradable, explaining the difference from the low strength wastewater. The BOD5/COD ratio of greywater in this study was within the range of 0.46 and 0.74 with an average of 0.60.

Table 3

Characteristics of raw greywater

Parameter Na Min value Max value Average Third class/primary treated wastewaterb Second class/secondary treated wastewaterb 
pH 35 5.77 7.96 6.71 6.5–9.0 6.5–9.0 
EC (ms/cm) 30 520.6 906 688 750–2,000 250–750 
Temperature (°C) 30 24.71 28.92 27.55 – – 
TDS (mg/L) 30 313 597 509.87 (±98) 2,500 2,000 
DO (mg O2/L) 30 0.89 2.43 1.35 (±0.3) – – 
TSS (mg/L) 35 50 125 95 (±43) 350 40 
COD (mg O2/L) 35 301 526 392 (±82) 600 80 
BOD5 (mg O2/L) 35 140 390 298.6 (±50) 300 40 
BOD5/COD ratio  0.465 0.741 0.60 – – 
TP (mg/L) 35 8.4 12.1 10.54 (±0.4) – – 
Nitrates (mg/L) 35 0.39 0.48 0.40 (±0.1) – – 
Nitrites (mg/L) 30 ND ND ND – – 
Ammonia-N (mg/L) 30 7.5 9.2 8.4 (±0.6) – – 
TKN (mg/L) 30 20 33 28 (±1.6) – – 
Oil and grease (mg/L) 35 90 152 118.5 (±40) Not limited 10 
Ca (mg/L) 30 151.41 437.61 290.36 (±52) – – 
Mg (mg/L) 30 83.22 140.01 105.64 (±53) – – 
Na (mg/L) 30 265 420 320.98 (±47) – – 
Number of cells or eggs of Nematoda (count/L) 
E. coli count (100/mL)   ND Not limited 1,000 
SARadj (%) 35 19.16 33.05 23.25 25 20 
Parameter Na Min value Max value Average Third class/primary treated wastewaterb Second class/secondary treated wastewaterb 
pH 35 5.77 7.96 6.71 6.5–9.0 6.5–9.0 
EC (ms/cm) 30 520.6 906 688 750–2,000 250–750 
Temperature (°C) 30 24.71 28.92 27.55 – – 
TDS (mg/L) 30 313 597 509.87 (±98) 2,500 2,000 
DO (mg O2/L) 30 0.89 2.43 1.35 (±0.3) – – 
TSS (mg/L) 35 50 125 95 (±43) 350 40 
COD (mg O2/L) 35 301 526 392 (±82) 600 80 
BOD5 (mg O2/L) 35 140 390 298.6 (±50) 300 40 
BOD5/COD ratio  0.465 0.741 0.60 – – 
TP (mg/L) 35 8.4 12.1 10.54 (±0.4) – – 
Nitrates (mg/L) 35 0.39 0.48 0.40 (±0.1) – – 
Nitrites (mg/L) 30 ND ND ND – – 
Ammonia-N (mg/L) 30 7.5 9.2 8.4 (±0.6) – – 
TKN (mg/L) 30 20 33 28 (±1.6) – – 
Oil and grease (mg/L) 35 90 152 118.5 (±40) Not limited 10 
Ca (mg/L) 30 151.41 437.61 290.36 (±52) – – 
Mg (mg/L) 30 83.22 140.01 105.64 (±53) – – 
Na (mg/L) 30 265 420 320.98 (±47) – – 
Number of cells or eggs of Nematoda (count/L) 
E. coli count (100/mL)   ND Not limited 1,000 
SARadj (%) 35 19.16 33.05 23.25 25 20 

EC = electrical conductivity, DO = dissolved oxygen concentration, TDS = total dissolved solids, TSS = total suspended solids, COD = chemical oxygen demand, BOD = biological oxygen demand, TP = total phosphates, TKN = total Kjeldahl nitrogen, SARadj = adjusted sodium absorption ratio, ND = not detected.

aN = number of samples.

bEgyptian regulation: Egyptian Environmental Affairs Agency (EEAA), Law 48, No. 61-63, Permissible values for wastes in River Nile (1982) and Law 9, Law of the Environmental Protection (2009).

It is worth mentioning that the average ratio of COD/NH3/TP has been reported typically as 100/5/1 for domestic wastewater (Metcalf & Eddy 2003). Furthermore, Kargi & Uygur (2003) calculated an optimum COD/NH3/PO4-P for a maximum nutrient removal in the activated sludge process for synthetic wastewater with a five-step sequencing batch reactor (SBR) of 145/5.87/1. On the other hand, Jefferson et al. (2000) measured the COD/NH3/TP ratio up to 1030/2.7/1 for greywater, indicating a macro-nutrient limitation. In the present greywater, the ratio of COD/NH3/TP is 37.2/0.80/1. The relatively high phosphorus concentration in the present greywater may be explained by the phosphorus-containing detergents used in Egypt.

Therefore, the characteristics of the present greywater are within the group that is classified as ‘primary treated water’ according to the permissible limits of Egyptian regulations (Egyptian Environmental Affairs Agency (EEAA) 2000) (Table 3). This raw greywater was previously studied extensively by Abdel-Shafy et al. (2014) and it was concluded that such water is allowed only to be reused for irrigating woody trees.

Treatment of raw greywater with UASB reactor

The results are given in Table 4. The UASB treated effluent showed that the TSS, COD, BOD, oil and grease, ammonia-N, TKN and TP were reduced from 109 to 88, 394 to 166, 235 to 76, 110 to 17.9, 7.95 to 6.83, 38 to 9.87 and 9.3 to 2.0 mg/L, respectively. The corresponding average percentage of removal was 19.3, 57.8, 67.5, 83.7, 14.1, 74 and 78.4%, successively (Table 4). It is worth noticing that the highest removal rate was exhibited by oil and grease (83.7%), which may be explained as the effect of the anaerobic treatment (i.e. degradation of organic load). For the TP, TKN and BOD5, reasonable removal was achieved that may be attributed to the consumption of the anaerobic bacteria in the anaerobic UASB system. By correlating the characteristics of the UASB treated effluent with the permissible limits of Egyptian regulations (Egyptian Environmental Affairs Agency (EEAA) 2000) (Table 3), it can be seen that it is still within the group that is classified as ‘third class primary treated water’. It is worth noticing that the BOD5/COD ratio of the treated effluent was 0.46 compared with 0.60 in the raw greywater. Furthermore, the average ratio of COD/NH3/TP improved in the treated effluent to 83/3.42/1 compared with 37.2/0.80/1 in the raw greywater. The typically reported ratio is 100/5/1 for domestic wastewater (Metcalf & Eddy 2003).

Table 4

Characteristics of raw greywater, effluent of UASB, effluent of MBR and the overall percentage of removal in correlation with the permissible limits of unrestricted water reusea

Parameters N Raw greywater (average) mg/L UASB effluent
 
MBR effluent
 
Total overall % of removal Permissible limits first class group for (advanced wastewater treatment)a Criteria for treated wastewater reuseb 
mg/L % of removal mg/L % of removal 
TSS (mg/L) 22 109 88 19.3 2.5 97.2 97.7 20 15 
COD (mg O2/L) 22 394 166 57.8 8.5 94.8 97.8 40 10 
BOD5 (mg O2/L) 22 235 76 67.5 6.1 92 97.4 20 <10 
Oil and grease (mg/L) 22 110 17.9 83.7 4.6 74.3 95.8 
TP (mg/L) 22 9.3 78.4 0.95 52.5 89.8 – 2.0 
Ammonia-N (mg/L) 22 7.95 6. 83 14.1 0.44 93.6 94.5 0.5 0.5 
TKN (mg/L) 22 38 9.87 74.0 2.3 76.47 93.9 –   
E. coli count (100/mL) –  – <100 – – 100 2.2 50%, 12 80% 
Number of cells or eggs of Nematoda (count/L) ND ND – zero – – Not detectable 
Parameters N Raw greywater (average) mg/L UASB effluent
 
MBR effluent
 
Total overall % of removal Permissible limits first class group for (advanced wastewater treatment)a Criteria for treated wastewater reuseb 
mg/L % of removal mg/L % of removal 
TSS (mg/L) 22 109 88 19.3 2.5 97.2 97.7 20 15 
COD (mg O2/L) 22 394 166 57.8 8.5 94.8 97.8 40 10 
BOD5 (mg O2/L) 22 235 76 67.5 6.1 92 97.4 20 <10 
Oil and grease (mg/L) 22 110 17.9 83.7 4.6 74.3 95.8 
TP (mg/L) 22 9.3 78.4 0.95 52.5 89.8 – 2.0 
Ammonia-N (mg/L) 22 7.95 6. 83 14.1 0.44 93.6 94.5 0.5 0.5 
TKN (mg/L) 22 38 9.87 74.0 2.3 76.47 93.9 –   
E. coli count (100/mL) –  – <100 – – 100 2.2 50%, 12 80% 
Number of cells or eggs of Nematoda (count/L) ND ND – zero – – Not detectable 

aEgyptian regulation: Egyptian Environmental Affairs Agency (EEAA), Law 48, No. 61–63, Permissible values for wastes in River Nile (1982) and Law 9, Law of the Environmental Protection (2009).

bAmendment of law 48/1982 in 2013 (criteria for treated wastewater reuse in agricultural irrigation of crops including vegetables eaten uncooked).

ND = not detected.

Oil and grease are considered difficult compounds to degrade in anaerobic process. However, elimination was recorded for oil and grease as well as BOD5 and TP at a reasonable rate by UASB. This may be explained by the hydrolysis of the organic load in the UASB anaerobic system (Lettinga et al. 1980; Ghangrekar et al. 2002; Abdel-Shafy et al. 2009).

Correlation between the present study and the previous investigation (Abdel-Shafy et al. 2014) with respect to the efficiency of UASB and the sedimentation system using two successive tanks for treatment of the same raw greywater is given in Table 5. The achieved elimination by the sedimentation tanks, for a period of 1.5 h, in terms of TSS, COD, BOD and oil and grease, was 55.9, 14.4, 10.8 and 11.3%, respectively. Increasing the sedimentation period to 4.5 h increased the removal rates to 66.5, 40.3, 38.3 and 49.8 successively (Abdel-Shafy et al. 2014). The corresponding elimination rates by UASB reached 19.3, 57.8, 67.5 and 83.7% (Table 5). The comparison reveals that UASB is a more efficient process for COD, BOD and oil and grease, with higher removal rates. The highest efficiency was recorded for the removal of oil and grease. In contrast, UASB was less efficient for the removal of TSS. Therefore it was essential to use the MBR system, which was highly efficient for the removal of the pollution parameters.

Table 5

Correlation between the efficiency of up-flow anaerobic sludge blanket and sedimentation using two successive tanks for treatment of raw greywater

Parameters UASB effluent
 
Two successive STa (for a period of 1.5 h)
 
Two successive STa (for a period of 4.5 h)
 
Concentration % of removal Concentration % of removal Concentration % of removal 
TSS (mg/L) 88 19.3 60.6 55.9 46 66.5 
COD (mg O2/L) 166 57.8 397 14.4 277 40.3 
BOD5 (mg O2/L) 76 67.5 348 10.8 240 38.3 
Oil and grease (mg/L) 17.9 83.7 225.3 11.3 126.5 49.8 
Parameters UASB effluent
 
Two successive STa (for a period of 1.5 h)
 
Two successive STa (for a period of 4.5 h)
 
Concentration % of removal Concentration % of removal Concentration % of removal 
TSS (mg/L) 88 19.3 60.6 55.9 46 66.5 
COD (mg O2/L) 166 57.8 397 14.4 277 40.3 
BOD5 (mg O2/L) 76 67.5 348 10.8 240 38.3 
Oil and grease (mg/L) 17.9 83.7 225.3 11.3 126.5 49.8 

ST = sedimentation tanks (for a period of 1.5 h and/or 4.5 h).

Treatment of UASB effluent by membrane bioreactor

When the anaerobic effluent of the UASB was directed to the aerobic MBR system, efficient removal of the pollution parameters was achieved (Table 4). The final concentration of TSS, COD, BOD5, oil and grease, ammonia-N, TKN and TP in the effluent was 2.5, 8.5, 6.1, 4.6, 0.44, 2.3 and 0.95 mg/L, respectively. The corresponding removal rate reached 97, 94.8, 92, 74, 93.6, 56.4 and 52.5% successively (Table 4). Ammonia oxidation with an efficiency of 93.6% removal was achieved in this system. This result is in good agreement with that reported by Scholz & Fuchs (2000) and Qin et al. (2007). The biodegradability–BOD5/COD ratio in the MBR effluent increased to 0.72 compared with 0.46 in the influent.

Oil and grease are regarded as two of the main foulants in MBR. The present experiments were carried out in the reactor operated under aerobic conditions. The continuous aeration provided for MBR limited membrane fouling and maintained the aerobic condition of the reactor as well as enhanced the oxidation of ammonia and any other slowly degradable pollutants, including detergents and oil and grease. This effective aeration could maintain floating of oil and grease on the water surface and prevented any material adhering on the surface of the MBR. Meanwhile, the aerobic activated sludge could eliminate oil and grease at a reasonable rate of 74.3%. It was reported by Scholz & Fuchs (2000) and Qin et al. (2007) that oil and grease were eliminated in oil-contaminated wastewater by more than 90% by MBR. This effect can meaningfully be ascribed to a permeate quality, complete elimination of TSS, in which pollutants are adsorbed. Similarly, reduction of COD exceeding 94% was obtained by Scholz & Fuchs (2000) for treatment of oil-contaminated synthetic wastewater (COD ranging from 5,262 to 7,877 mg/L) in MBR.

Figure 2 demonstrates the decrease in level of TSS, COD, BOD5 and oil and grease in the effluent of UASB and the effluent of MBR in correlation with their level in the raw greywater. It is worth mentioning that the characteristics of the final treated effluent could successfully meet the permissible limits of both the unrestricted water reuse according to the Egyptian Environmental Affairs Agency (EEAA) (2000) and the Amendment (2013).

Figure 2

Level of TSS, COD, BOD5 and oil and grease in the effluent of UASB and the effluent of MBR in correlation with their level in the raw greywater.

Figure 2

Level of TSS, COD, BOD5 and oil and grease in the effluent of UASB and the effluent of MBR in correlation with their level in the raw greywater.

Overall results reveal that the characteristics of the raw greywater can be classified as ‘third class primary treated water’ according to the permissible limits of Egyptian regulations (Egyptian Environmental Affairs Agency (EEAA) 2000) that is the water is allowed to be reused for irrigating woody trees only. When such greywater was subjected to UASB treatment, elimination of COD and BOD at the rate between 55 and 65% was achieved. It is well known that oil and grease are considered difficult compounds to degrade by the anaerobic process. However, the UASB system was successful for eliminating oil and grease, TKN and phosphates at a rate of between 74 and 83%. However, the treated effluent was classified as ‘third class primary treated water’. Further treatment by MBR could achieve remarkable progress in the removal of all pollution parameters where the removal of the TSS, COD and BOD ranged from 92 to 97%. The overall removal of all the pollution parameters ranged from 94 to 97%. The final effluent could successfully reach the permissible limits of unrestricted water reuse according to Egyptian Environmental Affairs Agency (EEAA) (2000) and the Amendment (2013).

CONCLUSION

The use of UASB as a primary anaerobic treatment proved to be efficient in the elimination of oil and grease, phosphates, nitrogen compounds as well as the organic load (BOD and COD). The system also eliminated the sludge through the organic degradation by the anaerobic system. UASB proved to be more efficient in elimination of COD, BOD and oil and grease, but less efficient in TSS removal. The obtained results suggest that the MBR system is technically feasible for greywater treatment and it can efficiently replace the conventional treatment process. Employing a combination of UASB and MBR as hybrid treatment system proved to be very effective in reaching the unrestricted water reuse criteria. The studied integrated systems demonstrated efficient final treated effluent in terms of physico-chemical characteristics. The performance of the studied integrated system could be a guide for a potential full-scale application. The advantage is water reuse for unrestricted purposes.

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