Rapid urbanisation is generating large amounts of industrial wastewater, polluting water bodies in India. A number of micro, small- and medium-scale enterprises (MSMEs) are contributing significantly to this pollution.
According to the MSME Development Act 2020, industries requiring up to 1 crore of the investment are classified as micro, industries requiring up to 10 crores of investment are classified as small, and industries requiring up to 20 crores of investment are classified as medium-scale industries.
However, the main concern with MSMEs has been the quality and quantity of industrial wastewater that they generate and their inability to establish treatment plants on an individual basis due to lack of space and financial resources.
Common Effluent Treatment Plants (CETPs) are suitable for small and medium-sized units and the Ministry of Environment, Forest and Climate Change, Government of India, has asked various state pollution control boards to set up CETPs in various industrial areas in their respective states. A total of 193 CETPs serve over 212 industrial areas and estates in the country at present. The installation cost is mutually financed by the Central Government (up to 25 percent) the state government (up to 25 percent), and the member industries. A CETP receives effluent from the same industrial sector or from various industries from different sectors.
Although CETPs are designed and operated for efficient functioning, the quality and quantity of the effluent they receive vary daily and seasonally and can influence the treatment efficiency of the units.
The city of Ahmedabad in Gujarat, India, faces severe challenges in terms of industrial water management and river pollution and the Sabarmati river in Ahmedabad is known to be a critically polluted river under Category I by Central Pollution Control Board. Different types of industries exist in the area and affect the treatment efficiencies of the CETPs in these areas. However, very little information exists on the efficacy of these CETPs.
This study titled 'Assessing the effectiveness of Common Effluent Treatment Plants (CETPs) in the state of Gujarat, India Using Reliability Analysis' published in Cleaner Water aimed at assessing the effectiveness and reliability of seven CETPs in Ahmedabad in terms of their quality of wastewater treatment. Conventional parameters of Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Suspended Solids (SS), Ammoniacal Nitrogen (NH3-N) and Phenolic Compounds (PC) were used to assess the overall functioning of CETPs.
The CETPs in Ahmedabad are permitted by the GPCB to allow effluent with inlet physicochemical parameters as COD to be2000mg/L; BOD at 700mg/L; SS at 300mg/L; NH3-N, 50mg/L and PC -1mg/L. Only one of the STPs, (NTIEM) has inlet parameters of 1200mg/L and 500mg/L for COD and BOD, respectively.
The study found that:
The reliability of CETPs was variable
The results revealed significant variations in the reliability levels across all CETPs. The reliability levels ranged from 7 - 99.99 percent for COD, 25.5–99.99 percent for BOD, 46.8–99.4 percent for suspended solids, 41.2–99.8 percent for nitrogen, and 85.2–98.1 percent for phenolic compounds. This was mainly due to improper functioning of majority of CETPs.
There were variations in the quality of the influent entering the CETPs, the treated effluent discharged at the outlet, and the overall removal efficiencies of the CETPs.
Inlet concentrations of effluents
Variations were observed at the inlet concentrations of effluents due to changes in the functioning and processes of individual industries, shutting down of units due to low demand, and product change. All CETPs received influent wastewater in accordance with inlet standards, except for two (GVMM and NEPL) which consistently received higher concentrations of nitrogen due to insufficient preliminary treatment by the small industries before discharge into CETPs, coupled with high hydraulic and organic pollutant loads.
Output performance of CETPs
Only one CETP (NTIEM) showed consistent output in terms of the quality of treated discharge effluent, whereas the other CETPs showed significant variations in pollutant concentrations at the outlet.
Removal efficiency of the CETPs
The overall removal efficiency values for COD were greater than 50 percent for all CETPs except for one - OGEPA, which had an average COD removal efficiency of 41 percent. Most of the CETPs were able to reduce BOD concentrations by up to 50 percent compared with their influent concentrations.
Two CETPs (NDES and OGEPA) exhibited poor removal efficiency of less than 50 percent for suspended solids which showed that suspended solids were increasing at the outlet as compared to the inlet. This could be because of process issues or poor activated sludge removal, which could have contributed to the solids.
Only three CETPs (NTIEM, OEPL, and TGES) showed average removal efficiencies greater than 50 percent for nitrogen. The concentration of nitrogen in the discharged effluent increased as compared to the concentration of influent wastewater in several CETPs. Low supply of oxygen in the aeration tank, microbial degradation could have led to ammonification, increasing nitrogen at the outlet. CETPs typically displayed removal efficiency of more than 50 percent for all parameters.
Current reliability levels of CETPs
CETPs showed low reliability in terms of COD, BOD and SS, indicating that the treatment processes for the CETPs were not effectively treating the wastewater and not complying with the discharge standards.
CETPs were more likely to fail or were unreliable in meeting discharge limits due to various factors such as influent quality and quantity, sudden peak and shock loads, and treatment unit failure.
It was thus found that CETPs were inadequate in treating wastewater to discharge standards and were constantly releasing untreated wastewater into the Sabarmati river, damaging the river downstream.
What can be done to improve performance of CETPs
The study makes the following recommendations:
Reducing the amount of wastewater generated through process modification or effluent reuse and adequate treatment of effluents to meet the inlet standards of the CETP.
Constant monitoring of the quantity and quality and flow rate of wastewater at the inlet and outlet of the CETPs for critical parameters such as pH, COD, BOD using an online monitoring system.
Modifying and designing treatment schemes to meet the standards.
Improving the operation and maintenance of clarifiers by optimising the rake system, blasting, and coating all the metal surfaces, repairing their drive mechanisms, and covering the walls with protective material.
Keeping the mixed liquor volatile suspended solids content at the desirable level and focusing on specific contaminants, using bioaugmentation in the activated sludge process.
Optimising the aeration tank mixing intensity, dissolved oxygen levels, sludge age, and hydraulic retention time. Monitoring and adjusting the nutrient levels and upgrading the aeration system.
Regular monitoring of wastewater quality and treatment process parameters such as pH, temperature, and flow rate to ensure the optimal performance of the CETP.
Using treatment technologies such as membrane bioreactor, hydrodynamic cavitation, and Fenton’s reaction on a smaller scale and then on a larger scale for the upgradation or expansion of the CETPs.