Efficiency analysis of effluents treatment plants of different industries at Kalurghat – Port City of Bangladesh

Bangladesh has a great vicissitude limiting pollution by taking lessons from industrialized countries yet (Bafana et al. 2015; Hosen et al. 2015). Speedy industrial growth has greatly improved economic status as well quality of life, inversely has contributed awfully on environmental degradation (Centre for Policy Dialogue (CPD) 2002; Islam et al. 2013). Initially, industrial growth and development eventuated during then Pakistan reign; after 1971, government induced to denationalize all the industries, especially textile and fabrics to achieve more than profits (Bloom 2001; GoB 2011). Generally, effluent is considered to be pollution (e.g., the discharge from industrial works) but effluent water is used water (Jern 2006; Hannan et al. 2011; Prabha et al. 2015). Amidst different types of industries, wet processing of textiles, steels, paper, fertilizers, cements, and pharmaceuticals produce huge quantity of effluents (Akbari et al. 2002; Khan & Noor 2002; Bhandari et al. 2016; Ra et al. 2016). Consequently, pollution from industrial effluent is one of the major environmental concerns recently faced by the country (Kapley & Purohit 2009; Bafana et al. 2015). Thereby, it requires on-site treatment before releasing into public sewage system (Emongor et al. 2005; Xu et al. 2016).

The key environmental issues inter-linked with textile manufacturers are use of water, its treatment and disposal of liquid effluents (Wynne et al. 2001; Prabha et al. 2015; Morali et al. 2016). Here, dyes are contributing to overall toxicity at all processing stages; therefore, it is responsible for high level of biochemical oxygen demand (BOD), chemical oxygen demand (COD), color, surfactants, fibers, turbidity, and contains toxic heavy metals (Environmental Protection Authority (EPA) 1998; Belhaj et al. 2014; Silva et al. 2014). In addition, dyeing process usually contributes chromium, lead, zinc and copper to effluents (Benavides 1992; Nergus et al. 2005). Hence, the released effluents from the Effluent Treatment Plants (ETPs) of industries must meet the national effluent discharge quality standards (DoE 2008; Khan et al. 2009a) where Common Effluent Treatment Plant (CETP) facilitates the industries in easier control of pollution with low-cost as well acts as a step towards cleaner environment. Inasmuch efficiency and effectiveness of an ETP is very important (Khan et al. 2009b; Bafana et al. 2015), so the CETP is a better and economically viable option for industrial effluents treatment (Tufekci et al. 2007; Bhattacharya et al. 2016).

There are, currently, above 30,000 industrial units in Bangladesh; thereof, about 24,000 are small and cottage industries (DoE 2006; Ahmed & Nizamuddin 2012). The Department of Environment (DoE), recently, has identified 900 large polluting industries, have no treatment facilities for effluents and straightly discharge to adjacent soils and water bodies (Islam et al. 2006; Prabha et al. 2015); else, release their daily generated wastes into the ecosystem, on which local people depend on for their livelihoods (Chowdhury & Clemett 2006; Ra et al. 2016). Amidst, textile is one of the most important and rapidly developing industrial sectors in Bangladesh based on earning foreign exchange and labor employment (BTMC 2012). But these industries generate commingled a large quantity of contaminated effluents that pollute the environment (Akbari et al. 2002; Awomeso et al. 2010). To mitigate the risks associated with the discharge of textile effluents, an ETP is required (Khan et al. 2009a; Prabha et al. 2015) but due to high installation and operation cost, most of the textile industries in Chittagong don't run ETP; occasionally, operate when buyers or DoE inspect the factory (Chowdhury & Clemett 2006). Anyway, recently many industries are making progress in establishing and operating their own ETPs to comply with national and international requirements (Khan et al. 2009a; Bhattacharya et al. 2016).

Regretfully, advanced wastewater treatment technologies; e.g. - advanced oxidation process, aerated lagoon, bioreactor, constructed wetland, membrane bioreactor, nano-technology, ion-exchange, desalination, and reverse osmosis etc. are not popular for industrial and municipal wastewater treatment in Bangladesh till now (BTMC 2012; Bhattacharya et al. 2016), inversely, technologically ahead countries are recovering valuable nutrients, elements and metals from wastewater but Bangladesh lags behind yet (Khan et al. 2009a; Prabha et al. 2015; Xu et al. 2016). Further, ETP, which is closely linked to remove excess level of different pollutants from industrial effluents, has not really been quested to explore their efficiency of effluents treatment hereto in Bangladesh. Therefore, the absence of any known study on the efficiency of established ETPs has coupled the problems. Thereat, efficiency analysis of ETPs is momentous to improve its current performance and so the research work was carried out to assess the efficiency of ETPs.

Samples were collected from two points (i.e., pre-treatment/inlet and post-treatment/outlet). Samples were collected diligently in a 1-litre plastic bottle and filled the total volume to avoid any air space inside the bottle and then locked in-favor-of accurate assessment of the effluents quality. Plastic bottles were first washed thoroughly with soda water (HNO₃ was not available), following distilled water before collecting the samples. Then the bottles were labeled accurately and preserved in ice cool temperature for testing the target parameters in the laboratory of WASA.

The required instruments for conducting the planned experiments are – beaker (i.e. 150 ml & 250 ml), measuring cylinder (i.e. 100 ml & 1,000 ml), funnel, dropping pipette, filter paper, stirrer, dissolve oxygen (DO) meter, Sension156 Portable Multiparameter, pH meter, conductivity meter, Spectrophotometer (Model-HACH: DR/4000 V), electric balance, reagent bottles, and volumetric flasks. In contrast, the required reagents are – dilution water; seed (mixed microorganisms solution); concentrated H₂SO₄; HgSO₄; Ag₂SO₄; KCN; C₆H₁₀O; standard 5.0 N NaOH, K₂Cr₂O₇, C₈H₅KO₄ (KHP), (NH₄)₂Fe(SO₄)₂·6H₂O, & buffer solutions; chloroform; and potassium 1, chromo Ver 3, Cu Ver 1, & Zinco Ver 5 buffer powder pillow.

It was measured by using sension156 Portable Multi-parameter and based on a measurement of conductivity that can be correlated with dissolved solids. A calibrated conductivity meter had to be completely submerged into sample (a small amount of representative sample). Then it was stirred gently for a while until the meter gave a stable total dissolved solid (TDS) reading in mg/L unit.

pH meter and sension156 Portable Multiparameter were used to measure acidity. At first pH meter was calibrated by using several types of buffer solutions (i.e. pH 4/7/10). Then the protective cap was removed and turned on the meter by sliding switch, on top of the meter. Then it was immersed into the solution to test, without exceeding the maximum level. The meter was gently stirred and waited for the reading to be stabilized. Similarly, DO and electric conductivity (EC) were measured by following same processes just different is DO meter and Conductivity meter were used respectively as substitute of pH meter and sension156 Portable Multiparameter.

Here, a = ml. (NH₄)₂.Fe(SO₄)₂·6H₂O required for blank, b = ml. (NH₄)₂.Fe(SO₄)₂·6H₂O required for sample, and N = normality of (NH₄)₂.Fe(SO₄)₂·6H₂O

It was carried out by diluting the sample with de-ionized water saturated with oxygen, inoculating it with a fixed aliquot of seed, measuring the DO and sealing the sample. The sample was kept at 20 °C in the dark to prevent photosynthesis for 5 days, and DO was measured again. The difference between the final DO and initial DO is the BOD; the apparent BOD for the control is subtracted from the control result to provide the corrected value.

Spectrophotometer (model- HACH: DR/4,000 V) was used to determine the quantity of Cr, Zn, Cu, Pb and Ni in the effluents. It is a multifunctional instrument that is used in WASA lab for measuring different water quality parameters. In case of Cr, at first 25 ml of sample was filtered by filter paper and then a cell of sample was filled with 10 ml of filtered sample. Contents of one ‘Chroma Ver 3’ reagent powder pillow were added to the sample cell (prepared sample) and swirled to mix. Similarly, another sample cell was filled with 10 ml of sample (blank). The prepared sample was placed into the cell holder and hexavalent Cr (Cr⁶⁺) was displayed in mg/L unit.

Here, 50 ml sample was filtered and then 25 ml graduated mixing cylinder was filled with 20 ml of filtered sample. A content of one ‘Zinco Ver 5’ reagent powder pillow was added to the sample cell (prepared sample) and was swirled to mix. 10 ml of the solution was poured into a sample cell (blank) and 0.5 ml of C₆H₁₀O was added respectively to the remaining solution. Then cylinder was stoppered and shacked vigorously for 30 seconds. During reaction, the solution from the cylinder was poured into sample cell (prepared sample). Similarly, the result was showed in mg/L Zn unit.

50 ml of sample was filtered and then a sample cell was filled with 10 ml of sample, following added the contents of one Cu Ver 1 reagent powder pillow to the sample cell (prepared sample) and swirled to mix. Then cylinder was stoppered and shacked vigorously for 30 seconds. Likewise, the result was displayed in mg/L Cu unit.

500 ml sample was filtered first and then a 250 ml graduated cylinder was filled to mark with sample and transferred into 500 ml through funnel. Then the content of one buffer powder pillow was added, citrated for heavy metals. It was stoppered and shacked to dissolve. Similarly, 50 ml of chloroform was added to a 50 ml graduated mixing cylinder; then the content of one Dithi Ver metal reagent powder pillow was added, stoppered and inverted repeatedly to mix. 30 ml of this dithizone solution was poured into a second graduated cylinder; similarly, 30 ml of the dithizone solution was added to the separator funnel. Opened stopcock to vent then close and 5 ml of 5.0 N NaOH standard solution was added, stoppered, inverted and again opened to vent. Then closed the stopcock and shacked the funnel once or twice and vented again. And continued adding 5.0 N NaOH standard solution drop-wise and shaking the funnel after every few drops until the color of the solution being changed from blue-green to orange. Then 5 more drops of 5.0 N NaOH standard solution were added and 2 heaping 1.0 g scoops KCN was added to the funnel then stoppered and shacked vigorously until the KCN was dissolved. Then pea size cotton was inserted into the delivery tube of the funnel and slowly drained the bottom layer into a dry 25 ml sample cell. Finally, stoppered the sample cell and filled another sample cell with chloroform (blank) and again stoppered. Similarly, the result was obtained in mg/L Pb unit.

Firstly 50 ml sample was filtered and then a sample cell was filled with 10 ml of deionized water (blank); again a second cell also filled with 10 ml of bath sample. The content of one potassium 1 reagent powder pillow was added to the sample (prepared sample). Then it was stoppered and shacked to dissolve. Analogously, the result was found in mg/L Ni unit.

Industrial effluents contaminate surface water, soil and groundwater due to presence of different pollutants (e.g., soluble solids, suspended solids, organic matter, heavy metals and toxic chemicals). Therefore, pre-treatment of discharged wastewater and determining the effluents quality is momentous (Prabha et al. 2015). The study was conducted to characterize the effluents quality of inlet and outlet of ETPs. So, the difference between inlet and outlet effluent's TDS and TSS values of the investigated industries are shown in (Table 1). The highest TDS value (2,687 mg/L) was found at Well Group while the lowest (276 mg/ L) at Royal Tec BD in inlet effluent; perhaps due to containing mobile charged ions including calcium bicarbonate, nitrogen, iron phosphorous, sulfur, and other minerals discharged from textile, washing and dyeing process. Inversely, TDS of outlet effluent varied from 247 mg/L to 2,001 mg/L and remained within the DoE standard limit (i.e. 2,100 mg/L) in all industries though individual values weren't analogous. Hence, it is crystal clear that pollution intensity and treatment efficiency is varied from industry to industry, because of using different types of chemical in textile dyeing and washing process along with followed different treatment methods (physical, chemical, biological and combined) as well expert technicians. Water having high TDS values can cause osmotic stress at the root zone of plants which makes more difficult for a plant to absorb water for growth; thereby, increased TDS in irrigation water leads to lower crops production (Mojiri 2011).

The maximum concentration (800 mg/L) of TSS was observed at Well Group but the minimum (331 mg/L) at Golden Height in inlet effluents while the rest industries effluents contained higher TSS in terms of DoE standard (i.e. 150 mg/L) (Table 2). TSS is mainly floating in nature and can be removed from the wastewater by physical treatment (i.e. screening). Inversely, the outlet effluents TSS varied from 26 mg/L to 221 mg/L where 6 out of 9 industries remained within the DoE standard but Mans Fashion (180 mg/L), Well Group (160 mg/L), and Alfa Textile (221 mg/L) were not within DoE prescribed water quality criteria. Anyway, a significant variation was observed both in inlet and outlet effluents of all industries due to difference of pollution intensity and treatment efficiency respect to TSS values. High TSS reduces light penetration and decreases photosynthetic rates of green aquatic macrophytes, algae and cells that are served as food sources for many invertebrates (Murphy 2007; Silva et al. 2014).

To evaluate the efficiency of ETPs in different industries, different chemical parameters (e.g., DO, BOD, COD, pH and EC) were analyzed in the study. Low DO concentrations (<3 mg/L) in fresh water aquatic systems indicate high pollution and cause negative effects on lives (Yayintas et al. 2007). Results showed (Table 2) that DO in inlet effluents differed from 1.2 mg/L to 3.6 mg/L where the highest DO (3.6 mg/L) was found at Golden Height but the lowest (1.2 mg/L) at Smart Jeans. The rest industries were also below DoE prescribed standards (i.e. 4.5–8.0 mg/L), probably due to the presence of chemically oxidized and biodegradable organic compounds in the effluents. The result also presented that DO in outlet effluents increased by all the industries against the inlet results due to the optimum rate of chemical dozing and bacterial activities during treatment while DO at Mans Fashion, Smart Jeans, Well Group, Alfa Textile and Asian Apparels industries still didn't fulfill the DoE requirement; inversely, Golden Height (4.7 mg/L), Royal Tec BD (4.8 mg/L), Chin Hung Fiber (4.9 mg/L) and Sanzi Textile (4.6 mg/L) industries fulfilled. Inasmuch DO levels below 4 mg/L in water puts aquatic life under stress, so reduced DO affects adversely on all aquatic lives. If DO levels remain below 1–2 mg/L for a few hours that can result in large fish kills (Singh et al. 1998); however, constructed wetland can facilitate to increase DO level in industrial wastewater (Xu et al. 2016).

From (Table 2), it is seen that in inlet the maximum concentration (240 mg/L) of BOD was observed at Smart Jeans while the minimum (72 mg/L) at Royal Tec BD; similarly the rest industries also generated higher BOD contents against the DoE standards (i.e. 50 mg/L). BOD value indicates the strength of the wastewater in which oxygen was consumed by microorganism in biodegrading the organic maters. The BOD in outlet effluent varied from 29 mg/L to 96 mg/L where BOD at Golden Height, Royal Tec BD, Chin Hung Fiber, Well Group, and Sanzi Textile industries remained within the DoE water quality standards, but crossed the limit by Alfa Textile (89 mg/L), Asian Apparels (79 mg/L), Smart Jeans (96 mg/L), Mans Fashion (78 mg/L). Else, the efficiency difference between inlet and outlet effluents was noticed in all industries. Excessive BOD is harmful to aquatic life (e.g., fish and microorganisms). It also causes bad taste to the drinking water and too high BOD level keeps water at risk for further contamination (Singh et al. 1998). A study in South-Eastern Tunisia found that effluent quality in terms of BOD was in agreement with water quality standard after treatment (Belhaj et al. 2014).

It was observed that the concentration of COD in inlet effluents differed from 291 mg/L to 442 mg/L among the studied industries (Table 2), where the highest value (442 mg/L) was found at Mans Fashion but the lowest at Smart Jeans (289 mg/L). Besides, all the industries generated higher value of COD compared to DoE standards (i.e. 200 mg/L). Generally, COD test gives an indication of the impact of discharged waters on aquatic life by means of depleting DO level. Result showed that COD contents in outlet effluents was varied from 111 mg/L to 282 mg/L where COD at Golden Height, Sanzi Textile, Royal Tec BD and Chin Hung Fiber industries remained within the DoE standards (200 mg/L), but exceeded the limit by other 5 industries, the highest in Alfa Textile (282 mg/L). In addition, a clear difference between inlet and outlet were noticed in all industries. Anyway, COD test is commonly performed to measure, indirectly, the quantity of organic compounds in water. From (Table 2), it is seen that the amount of COD was high in all industries before treatment depending on the types of fibers, dyes, and additives that were used in various industrial activities (Demmin & Uhrich 1998). Similarly, both inlet and outlet effluent's COD content varied significantly in all industries due to containing different chemically oxidized organic compounds and followed treatment facilities (Xu et al. 2007). Bhandari et al. (2016) found that the characterization of fertilizer wastewaters from different streams revealed huge variation in COD from 50 to 140,000 mg/kg in inlet that showed high reduction of COD (85%) after treating wastewaters in outlet and Silva et al. (2014) also found analogous results.

The study revealed that pH in inlet effluents differed from 3.8 to 12.2 where the maximum (12.2) and the minimum (3.8) pH value were found at Alfa Textile and Well Group respectively (Table 3). The variation of pH value is primarily caused by different kinds of dye stuffs and washing ingredients used in the dyeing and washing process in industries. Similarly, pH in outlet effluents varied from 6.8 to 10.2 where pH in all industries remained within DoE standards (i.e. 6–9) but differed from standard in Alfa Textile (10.2) industry. Anyway, the industries showed the better treatment efficiency, likely due to optimum chemical dozing. Besides, both the inlet and outlet effluent's pH varied may be for using different types of chemicals in the textile dyeing and wet processing along with optimum chemical dozing during the treatment process. Here, pH indicates the suitability of water for various purposes and toxicity to aquatic lives (Slokar & Le Marechal 1998). High pH reduces fish production (Argo 2003) and inhibits the growth of aquatic macrophytes (Edmund 1998). Similarly, low pH can destroy the fish population accompanied by decrease in the variety of species in food chain (Sharma 2003).

Similarly, the results showed that EC in inlet effluents differed from 552 μS/cm to 5,375 μS/cm where the highest (5,375 μS/cm) EC was found at Well Group but the lowest (552 μS/cm) at Royal Tec BD. The rest industries generated highly polluting effluents in terms of EC compared to DoE standards (i.e. 1,200 μS/cm) except Mans Fashion (824 μS/cm) and Golden Height (624 μS/cm) which may be due to presence of organic and inorganic matter with high ionic load (Table 3). The result of outlet effluents illustrated that in case of EC effluents quality improved within the DoE standard at Chin Hung Fiber (1,048 μS/cm) and Sanzi Textile (1,027 μS/cm) but the other industries still exceeded the standards without Royal Tec BD (495 μS/cm). Comparing all industries, both the inlet and outlet effluent's EC varied significantly probably due to inefficient rate of chemical dozing during effluents treatment in each of the industries. The increased EC in irrigation water leads to lower crops production; though EC itself is not a human or aquatic health concern but it can serve as an indicator of other water quality problems (Mojiri 2011).

Amidst 9 industries, some industries discharged water within the range of DoE permissible limit and some crossed in case of different chemical parameters. From (Table 4), it is seen that only 3 industries discharged water within the DoE prescribed limit for EC while Mans Fashion (1,243 μS/cm), Golden Height (1,762 μS/cm), Smart Jeans (1,927 μS/cm), Well Group (3,201 μS/cm), Alfa Textile (4,003 μS/cm), and Asian Apparels (1,973 μS/cm) crossed the limit. Similarly, all industries maintained pH value within DoE standard limit but Alfa Textile (10.2) crossed the limit. Belhaj et al. (2014) found the treated wastewaters pH within the national water quality criteria. In case of DO, 4 industries discharged water within DoE prescribed limit and 5 showed below the ranges viz. Mans Fashion (3.7 mg/L), Smart Jeans (3.2 mg/L), Asian Apparels (4.2 mg/L), Alfa Textile (3.6 mg/L), and Well Group (4 mg/L). Besides, 4 industries crossed DoE standard limit for BOD such as Mans Fashion (78 mg/L), Smart Jeans (96 mg/L), Alfa Textile (89 mg/L), and Asian Apparels (79 mg/L). Xu et al. (2016) found that combined constructed wetland showed better performance in case of reducing BOD and COD from industrial park wastewater. In addition, 4 industries maintained and the rest didn't maintain according to DoE prescribed water quality parameter for COD viz. Mans Fashion (225 mg/L), Smart Jeans (216 mg/L), Well Group (235 mg/L), Alfa Textile (282 mg/L), and Asian Apparels (221 mg/L). It was seen that ozonation treatment can reduce COD at 31–46% from industrial wastewater (Morali et al. 2016) while membrane filtration treatment showed better (i.e. 77–80%) reduction of COD (Bhattacharya et al. 2016).

The availability of toxic heavy metals in industrial wastewater limits its discharge into water bodies or for reusing (Ra et al. 2016). The evaluation of ETP's efficiency is very important to protect environment and public health from dangers of industrial wastewater. Hence, the efficiency of ETPs must be, regularly, monitored (Bafana et al. 2015) and present study evaluated the performance of ETPs of different industries at Kalurghat, Chittagong. From (Table 5), it is seen that the study was carried to analyze target heavy metals parameter (e.g., Cr, Pb, Zn, Cu, and Ni) of the outlet of ETPs; there is only Alfa Textile for (Cu, Zn, & Cr), Well Group for Cr and Asian Apparels for Ni that metals content were not within the DoE standards and in the rest industries such parameters were within the DoE prescribed water quality parameters. Prabha et al. (2015) found that the membrane bioreactor system was more efficient than conventional system in removal of Zn, Pb, and Cr from industrial effluents. Another study evaluated the performance of an industrial Wastewater Treatment Plant (WWTP) in South-Eastern Tunisia where average influent concentrations of Zn and Cr were 16 mg/L and 167.21 mg/L respectively. Results showed after treatment the effluent quality in terms of Cu and Zn levels were in agreement with standards, but Cr and Ni residual loads were still above the values required by Tunisian water quality criteria (Belhaj et al. 2014).

Most of the industries in Chittagong district don't have ETPs or the established ones are not run in a regular basis. Consequently, among 9 studied industries 4 industries, e.g., Royal Tech BD, Sanzi Textile, Chin Hung Fiber, and Golden Height (except EC) treat their effluent efficiently and discharge water within the DoE prescribed water quality standards. All others industries except Alfa Textile treat their effluent but not efficiently. This may be happened due to inefficient rate of chemical dozing, improper monitoring system and negative attitude towards running ETPs. As a result, all the parameters were not up to the standards. Untreated effluents from such industries, particularly from textile industries are one of the main reasons for the critical condition of the Karnafuli River in Chittagong.

This study was accomplished as a partial fulfilment of Master of Environmental Science degree of Institute of Forestry and Environmental Sciences (IFES), University of Chittagong, Bangladesh. Concluding the study especial thanks goes to classmates and respected teachers who cordially supported to make fruitful the entire study.