Efficiency evaluation of three fluidised aerobic bioreactor based sewage treatment plants in Kashmir Valley

The present investigation was conducted to monitor the physico-chemical characteristics and microbial load of sewage treatment plants (STPs) around the Dal Lake. The results show highly significant (P<0.001) reduction in some physico-chemical features and in microbial load at outlet of each STP. Order of reduction in all the STPs was found to be biochemical oxygen demand (BOD) > chemical oxygen demand (COD) > conductivity and fecal coliform (FC) > total coliform (TCC) > fecal streptococcus (FS) in the case of physico-chemical parameters and microbial characteristics, respectively. The overall performance of the wastewater treatment plant effectively removed TCC, FC and FS as follows, 52, 65 and 45%, respectively. Raw sewage showed insignificant (p>0.05) variation in some of the physico-chemical features and microbial load between the three STPs. Similarly, effluent also showed insignificant (p>0.05) variation in some of the physico-chemical features and microbial load, except conductivity which showed significant difference between the three STPs. Efficiency rates showed significant (p<0.05) differences in COD between the three STPs. The removal efficiency rate was not dependent on the type of STP and the year. It can be concluded from the study that the majority of physico-chemical features and microbial load exceeded the permissible limit as per Indian national standards. Therefore as per the results, it is suggested that the effluent should be pretreated before disposing into the environment. In addition, there is an urgent need to improve their efficiency rate by including advanced tertiary treatment processes such as rapid sand filtration, UV disinfection, chlorination, effluent polishing, construction of artificial wetlands, etc.


INTRODUCTION
Urbanization, industrialization, modernization as well as agricultural activities have put tremendous pressure on the limited freshwater resources, causing eutrophication and pollution of freshwater bodies all over the world.In recent times, abrupt increase in production and domestic use of organic chemicals has obliged sewage treatment plants (STPs) to improve their efficiency.Freshwater systems of Kashmir have not remained immune to the anthropogenic pressures and many of these, especially those located close to the human habitations, have deteriorated during the last 50 years.In addition to other anthropogenic activities, sewage discharges from STPs are considered a major contributor of contamination in this urban lake of Kashmir.
Wastewater is a major burden for water bodies and improper disposal of sewage leads to oxygen demand, increased nutrient concentration and promotion of toxic algal blooms leading to a destabilized aquatic ecosystem (Morrison et al., 2001).It has been seen by various agencies that India wastewater is comprised of high levels of organic, inorganic and microbial contaminants (Bohdziewicz and Sroca, 2006).So far, extensive work has been carried out to study the physico-chemical removal efficiencies of STPs, whereas there is less literature regarding the microbial load in wastewater treatment plants and their removal efficiency.Sewage from households is collected via a sewer system and flows to STP for treatment of chemicals and microbial load.The high level of fecal contamination and enteric viruses present in raw sewage is a major concern for public health and the environment; and therefore assessment of sewage is essential to safeguard the public health (Okoh et al., 2005(Okoh et al., , 2007)).
In most cases, STPs consist of two types of treatment systems: a physical and a biological purification steps.In physical purification, removal of the chemical is mostly due to sorption of chemicals to organic carbon.The effectiveness of the removal is directly related to the size and density of the particles.In the biological purification, removal is achieved by bacterial biodegradation, which mainly occurs via oxidation.At the end of the treatment processes, sludge and final effluent are released to the environment.Every chemical that enters the STP that is neither sorbed nor degraded will enter the environment via the effluent or evaporation from the STP.The priority objectives of wastewater treatment are to degrade organic wastes so that they do not cause oxygen demand in the receiving water body, remove nutrients to prevent eutrophication and protection of public health by destroying the pathogenic microorganisms (Gerardi, 2006;Akpor and Muchie, 2011).
Studies have shown that sewage treatment processes might also affect physico-chemical parameters of the final effluent such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), electrical conductivity, total hardness, alkalinity, dissolved oxygen, some metals and non-metal ions (Rawat et al., 1998;Adami et al., 2007).Although, various microorganisms in water are considered to be critical factors in contributing to numerous waterborne outbreaks, they play many beneficial roles in wastewater influents (Kris, 2007).In addition, purification processes remove pathogenic microorganisms (Reasoner, 1982Wang et al., 1966).Furthermore, microbiological indicators have been used for decades to monitor fecal pollution of water (Standard Methods, 1998).
Different studies have evaluated the efficiency of STPs and have compared the concentration of the chemical in the influent and that in the effluent.In most studies, significant reduction has been observed at outlet sites of STPs (Saha et al., 2012;Kumar et al., 2010;Desai and Kore, 2011).However, some studies have shown little or no reduction of pollutant concentration (Igbinosa and Okoh, 2009;Antunes, 2007;Momba et al., 2006;Akpor and Munche, 2011) which is a major concern for water bodies as well as public health.The comparative studies between STPs have shown both significant and insignificant variation (Jamwal et al., 2009;Kumar, 2010) in efficiency rates.In the past, some studies have also shown that STPs deviate from normal permissible limit which have been given by WHO and the United States Environmental Protection Agency (EPA) (Igbinosa, 2009;Antunes, 2007;Momba et al., 2006;Akpor, 2011).
Dal Lake receives effluent from the three STPs namely, Habak STP, Hazratbal STP and Lam STP as well as domestic wastewater from the surrounding settlements.These STPs were constructed by a private firm under the guidelines of Lakes and Waterways Development Authority (LAWDA) in 2004 at the cost of Rs 8.90 crore.In recent past, there has been debate on the working capability of these STPs.Although LAWDA seems to be satisfied with the working condition of these STPs, and claims that Dal lake's health would improve after all the STPs have started working, some analytical reports have raised questions about the working condition of these STPs.The research and monitoring division of LAWDA in August 2006, for example, reported increased nutrient concentration at the outflow stage, thus negating the claims made by LAWDA.So, knowing the above mentioned facts was necessary to perform a current monitoring survey on these STPs in order to know the present status of these STPs.
No past extensive study has been carried out to assess the efficiency and quality of these STPs.Because of the associated dangers of sewage, the present study was carried out to investigate the impact of the wastewater effluent discharged and to estimate the pollutant removal efficiency of STPs around the Dal Lake.We predicted that removal efficiency will depend on the characteristic features (working capability) of the individual STP, extent of aeration, hydraulic retention time, contact time and type of treatment used.In addition, microbial load will be greater in the influent than in the effluent (Figure 1).

MATERIALS AND METHODS
This study was conducted at three sewage treatment plants viz., Habak STP (34008ʹ50ʺN -74050ʹ36ʺE), Hazratbal STP (34°08ʹ06ʺN -74°50ʹ29ʺE) and Lam STP (34°07ʹ42ʺN -74°523ʹ36ʺE ) in the vicinity of Dal Lake with the design capacity of 3.2, 7.5 and 4.5 MLD, respectively (Table 1).All these plants receive domestic sewage and are treated using the fluidised aerobic bioreactor (FAB) biological treatment systems; a combined, dispersed and attached bacterial growth on fluidized media that is a modified version used in Germany, Netherlands, Europe and Canada successfully.This technology comprises of components like screening, grit removal, fluidised aerobic bioreactor followed by clarification and addition and precipitation to remove phosphates and chlorination (Figure 2).The final treated effluent is discharged into the lake.The water samples were collected on monthly basis for a period of 24 months between June 2010 and May 2012 for analysis of physico chemical features, in white plastic containers, which were previously sterilized with 70% alcohol and rinsed with distilled water.For microbial analysis, samples were collected seasonally at the three STPs.At the sites, the containers were rinsed thrice with the wastewater before being used to collect the samples.

Physico-chemical parameters of water samples
The influent and effluent water samples were collected between 10.00 and 15.00 h from all the sampling stations in 1 L polyethylene bottles.The parameters pH and conductivity were recorded on the spot.For the estimation of dissolved oxygen, separate samples were collected in separate glass bottles and fixed at the sampling sites in accordance with the Winklers method (APHA, 1998).BOD was determined by the 5 day test method, while COD determination was carried out using the open reflux method as per Standard Methods in APHA (1998).For removal efficiency of physicochemical parameters, inlet concentrations were subtracted from outlet concentrations for each parameter.

Microbial examination of water samples
Microbiological examination of samples was conducted promptly as possible (within 24 h) after collection or were stored at 4°C in a refrigerator until use.Serial dilutions were prepared immediately after sample collection.The proper dilutions for various bacterial groups were selected so that number of colonies on plate was between 30 and 300 using spread plate method.A multiple tube fermentation technique or most probable number (MPN) technique was used to determine the bacterial indicators as faecal coliforms (FC) and faecal streptococci (FS) according to standard methods described in APHA (1998).Multiple tube fermentation method used in the present work included measurement of total plate count and MPN of coliform.After incubation for 24 h at 35°C, results were recorded when acid and gas liberated in Durham tubes had changed in color to yellow.The spread-plate method was used for all counts.FC agar and FS agar were used for enumeration of faecal coliform and faecal streptococci.Each test was done in triplicate and the geometric means were recorded.The removal efficiency of bacterial indicators was calculated using the following formula:

Statistical analysis
Students t test was used to assess the significant variation between the raw influent and the effluent in the different STPs.One way ANOVA test was used to analyze the significant differences in influent and effluent between the three STPs.Similarly, efficiency rate between the different STPs was tested by using one way ANOVA test.
All statistics were carried out with the SPSS 11.5 statistical software package with significance levels set at P<0.05.

RESULTS
The data shows highly significant differences (P<0.001) in physico chemical features and microbial data between the inlet and outlet samples (Tables 2 and 3; Figures 3  and 8).Statistically, insignificant differences were observed in raw sewage and effluent between the three STPs (P>0.05)(Tables 4 and 5).Similarly, insignificant differences were observed in the efficiency rate of   different physico chemical features and microbial loads between the three STPs (P>0.05),except COD, which showed significant variation between the three STPs (F = 4.6; P = 0.013) (Table 6).

DISCUSSION
Although data shows significant differences in physico-chemical features and microbial load between the inlet and outlet, nevertheless, these variations do not meet the Indian national standards.As per Indian standards, to discharge effluents into water bodies, BOD, COD and faecal coliform should be less than 30 and 250 mg/L and 2500 MPN/100ml, respectively.The insignificant differences observed in the efficiency rate between the three STPs may be due to the fact that the same treatment technologies are employed for treatment of sewage at the three plants.Jamwal et al. (2009) while evaluating the efficiency of STPs in Delhi observed that effluents from all STPs exceeded FC standard of 10 3 MPN/100 ml for unrestricted irrigation criteria set by the National River Conservation Directorate (NRCD).However, they investigated STPs which were using different types of technologies including activated sludge process (ASP), extended aeration (EA), BIOFORE, trickling filter and oxidation pond for the treatment of sewage.In our case, all STPs used the FAB based technology, which is a recent technique for removal of pollutants from municipal sewage.The comparatively low efficiency rate in the three STPs may be due to the fact that primary sedimentation is not carried out in these STPs and as such, the efficiency rate of pollutant removal is affected.Furthermore, the high bacterial load in the effluent may be attributed to the fact that an appropriate dose of chlorine for disinfection is not given to the effluent.The results show that faecal streptococci are more resistant and persistent even after chlorination as compared to faecal coliforms.These results coincide very well with the findings of Cohen and Shuval (1972).The reduction of microbes depends on protozoan predation, settlement of suspended solids, inactivation due to sunlight, activity of filamentous bacteria, turbidity and sedimentation.
It seems from the results that pH increased slightly from raw to final effluent which may be due to the reduction of free CO 2 level in final effluent and addition of polyaluminium chloride.The pH range recorded for all the sampling sites lie within the WHO pH tolerance limit, that is, 6 to 9 for wastewater to be discharged into water body.Our results coincide with the findings of Morrison et al. (2001) who also found increase in pH level during treatment process.Occasional absence of DO concentration in sewage was recorded in some STPs due to heavy organic loading and septic conditions.Kumar et al. (2010) found similar sewage characteristics while working on two STPs in Karnataka.The DO concentrations of the effluents in our study were less than 5 mg/l.Consequently, these water sources would not be suitable for use of aquatic ecosystems (Rao, 2005).However, there was a slight increase in the effluent DO content due to the treatment processes, which may reduce the amount of impurities present in sewage through oxidation of organic matter (Prescott et al., 2002).
The high values of conductivity in raw sewage in the present study indicate increased salt concentration and pollution level of STPs.Reduction in BOD in all STPs during the treatment process may be due to the oxidation of organic matter by microorganisms that are used in FAB treatment as well as coagulation and flocculation brought about in the Claritube settler, which is a clarification cum flocculation chamber.Similar results were observed by Jamwal et al. (2009).The percentage removal of BOD in all the STPs was 67.86 ± 2.6 to 70.00 ± 3.6%, which is below the expected value of 85 to 90%, thus showing that BOD reduction is less than the expected.The same rate of reduction in BOD in all STP's could be due to similar technology which is currently used in all three STPs.COD shows similar trend as BOD.The significant variation in efficiency rate in COD between three STPs could be due to different types of sewage coming from different catchment areas.
Similarly, results show decrease in COD level at outlet during the treatment process due to the above mentioned facts.High COD and BOD concentration observed in the wastewater might be due to the use of chemicals, which are organic or inorganic that are oxygen demanding in nature (Akan et al., 2008).The values for most of the parameters in the discharged effluent were almost higher than the acceptable limits.This shows the inefficiency of the treatment plant in removing the pollutants in the sewage.
Tertiary treatment methods are essential to remove nitrogen, phosphorus, suspended solids, dissolved solids, refractory organics and heavy metals.Tertiary treatment process involves the addition of certain chemicals such as alum and polyelectrolytes which convert the dissolved substances into a solid settle able form.These chemical coagulates, mix up with the sewage water to form an insoluble gelatinous floc of suspended solids which settles down quickly.
In our case, it was observed that tertiary treatment is not capable of removing pollutants to a large extent.The reason may be inflow of sewage beyond designed capacity and improper maintenance and lack of expertise in the field.
The high coliform count in raw sewage obtained in our results may be an indication that the sewage is comprised of faecal matter coming from household latrines (APHA, 1998).The presence of pathogenic bacteria in treated wastewater effluent is a potential public health hazard, as this water source is directly discharged in receiving water bodies and may be used by communities for multiple purposes.At the inlet, physicochemical parameter values are relatively high which causes microbial biomass development, in particular, increases in faecal coliform and faecal streptococci (Rajib et al., 2011).It is clear from our results that some amount of load is retained even after the purification treatment process.So, it is essential to include a tertiary treatment step in STPs so that the purification process results in bacterial concentrations that are in compliance with discharge (Koivunen et al., 2003).

CONCLUSION AND SUGGESTIONS
All the municipal wastes that may have otherwise gone untreated into the environment are restricted from entering.Thus, these treatment plants play an important role in the control of pollution level.The results show highly significant reduction in some of the physic chemical features and microbial load.However, performance of these STPs do not meet the permit standards set by the Indian standard and WHO.Therefore, it is suggested that authorities should improve their efficiency capability by including tertiary treatment processes such as rapid sand filtration, UV disinfection, artificial lagoons, wetlands, adequate contact time, etc.In addition, there is need of trained and technical staff for proper monitoring and operation of these STPs in a standardized manner.Furthermore, regular monitoring of these STPs by national experts is necessary in order to improve the operational capability of these STPs.

Fig. 1 .Figure 1 .
Fig.1.Hypothesis showing that microbial load decreases as the wastewater proceeds through the treatment processes.

Fig. 2 Figure 2 .
Fig.2 Process flow diagram for FAB based sewage treatment plants.

Figure 3 .
Figure 3. Conductivity of influent and effluent sewage from different STPs.

Figure 4 .
Figure 4. BOD of influent and effluent sewage from different STPs.

Figure 5 .
Figure 5. COD of influent and effluent sewage from different STPs.

Table 1 .
Details of sewage treatment plant around Dal Lake (LAWDA).

Table 2 .
Physico chemical characteristics of raw sewage and effluent.

Table 3 .
Microbial load in sewage and effluent.

Table 5a .
Results of ANOVA test in raw sewage between three STPs.

Table 5b .
Results of ANOVA test in effluent between three STPs.

Table 6 .
Results of ANOVA test in efficiency rate between three STPs.