When we were given this assignment, BGPL was facing a serious problem of wastewater disposal and around 30 acres of land was wasted in disposing wastewater partially treated through Aerobic Treatment Technology. Ground water contamination, pathetic housekeeping and a smelly environment were only a few of the many problems.

Most of the companies in India are using only the Aeration Treatment System, which requires huge energy input for pumping oxygen and draining valuable electricity which could be otherwise used for a more effective purpose. I strongly believe that a detailed survey in this regard is necessary to explore the hidden potential. The findings and feedback need to be sent to the policy makers and various government departments, especially the Pollution Control Board, for necessary action.

A brief description of each stage of the process flow of treatment of, the Effluent Treatment Plant (ETP) schematic arrangement.

Influent Collection System: The influent generated from various production processes, utilities, washing, cleaning and also domestic uses is transferred using an underground pipeline through gravity pressure. The underground drainage system is provided with screens and a manhole chamber to retain fibrous particles and clean them periodically.

Collection Sump: The entire influent is received in an underground collection tank through gravity and the slurry is kept in a homogenous condition. There is continuous slow speed stirring to ensure that no settlement takes place in the tank. The tank is fitted with slurry pumps to pump out the thick slurry to the next stage of treatment.

Grit Chamber: The grit chamber retains grit/stone particles and stops them from going into ETP. There is a provision to operate one grit chamber and keep the second one as standby for cleaning. The effective removal of fibrous particles and stone particles ensures trouble-free operation of pumps in subsequent stages of treatment.

Equalization: A ground level sump receiving wastewater from the Grit Chamber equalizes the fluctuation in the influent quality by providing a retention time of 8 hrs. The wastewater quality is homogenized in this tank and uniform characteristics of influent are made available to the next stage of treatment. This tank not only ensures uniform quality of influent to the secondary treatment but also supplies continuous availability of wastewater to the biological treatment process of the ETP. During the process of equalization, sludge settles at the bottom of the tank, which is then removed periodically through sludge takeoff pipelines for its final disposal through the filter press, whereas the supernatant goes though gravity into the next stage of treatment.

Neutralization: An online neutralization system with the provision of compressed air turbulence and on line chemical dosing system ensures pH correction of normally alkaline influent from 8-12. The acid dosing tank provides flexibility to vary chemical dosing rate as per the need. The outlet water quality from the neutralization system should be uniform on pH scale and well within the limit of 7 to 8.5.

Primary Clarifloculation: The primary clarifloculation system is fitted with provision for Polyelectrolyte dosing, a floc preparation chamber with a slow agitation arm and a settling zone with a bottom-scraping arm for continuous removal of coagulated sludge from the bottom using semi-open impeller pump. The primary clarifloculator is also fitted with mechanized oil skimmer to continuously skim off the floating oil and floating impurities and push them into the oil box for its final removal from the wastewater stream. The clear water overflows from the primary clarifloculator to the next stage of treatment.

Buffer Tank: The equalized, neutralized, and clear wastewater is transferred from the primary clarifloculator through gravity into the Buffer tank. The Buffer tank provides uniform availability of equalized and neutralized water to the secondary treatment stage, which is a biological treatment process. The Buffer tank also provides seeding of anaerobic culture by receiving bottom slurry from UASB thickener. The anaerobic condition prevails in this tank due to the downward flow and presence of anaerobic bacteria. The Buffer tank is fitted with centrifugal feed pumps to parallel feeding of effluent into two UASB digesters.

Anaerobic Treatment: The UASB digesters (2 Nos.) treat organic contaminants present in the wastewater in the absence of oxygen using anaerobic bacteria. The flow dynamics is maintained within the digester in such a way that a sludge blanket (colony of anaerobic bacteria) is developed, which remains under suspension stage. Anaerobic bacteria digest the organic contaminants present in the wastewater and the percentile COD reduction across this stage is 70. The Anaerobic treatment process liberates Biogas, which is rich in methane content, and is combustible in nature. The digester design provides flexibility to recover the biogas if desired and use it for any thermal and electrical application. The Anaerobic digester is equipped with a bottom-flushing system and slurry take off system to ensure uniform flow across the entire cross section of the digester and periodical removal of dead sludge to sludge drying beds.

Anaerobic Sludge Thickener: The supernatant from the UASB reactor is passed through a gravity sludge thickener (2 Nos.) to recycle the sludge (Bacteria) back to anaerobic digester and allow clear supernatant to flow into a secondary aeration system. This also provides flexibility necessary to regulate the flow across the UASB digester by adjusting valves of recycling stream.

Aeration Tank: The balance organic contaminants present in outlets of the UASB digester are treated aerobically by compressed air supply through lobe type compressors. The aeration system consists of fine bubble diffusers that supply oxygen into the aeration tank for maintenance and survival of aerobic bacteria measured and maintained in terms of mixed liquor suspended solids (MLSS). The aerobic bacteria stipulates the organic load present in wastewater and multiplies via cell growth. The excess cells are rejected from the system to the sludge drying beds. The supernatant from the aeration tank is rich in MLSS content which must be segregated in order to obtain clear treated water, which is achieved in subsequent treatment process.

Secondary Clarifier: MLSS from the treated water at the outlet of an aeration tank is transferred through gravity into a secondary clarifier where the sludge is settled out and separated from an effluent stream. The supernatant from the secondary clarifier is a clear, transparent water, whereas the bottom thick slurry consisting of MLSS—that is recycled back to the Aeration tank to maintain its desired percentage and excess sludge—is rejected to sludge drying beds using semi-open impeller slurry pump for drying and dewatering.

Solid Waste Management: The thick slurry is collected from the Grit chamber, Equalization tank, Primary Clarifloculator, Secondary clarifier and UASB bottom flush and then pumped into a filter press for mechanized dewatering. The filtrate is transferred to a buffer tank, while the solid cake is collected into a trolley for final disposal though vermi-compost

Treated Effluent Collection and Distribution: The treated effluent from secondary clarifier conforms to the norms laid by the PCB. It is collected into a sump for further distribution/recycling into gardening/horticulture/washing and cleaning using a self-priming distribution pump. q 

Shreyans Energy (P) Ltd,

Jabalpur. MP. (India)

shailendrajain@shreyansenergy.com

Mobile: 09300644224