Feasibility Report for Water Pollution Control

Dr. Akepati S. Reddy

Thapar Center for Industrial Research & Development Patiala (PUNJAB) – 147 004

INDIA

Feasibility Report for Water Pollution Control

1. Introduction

The Oil and Fats unit has been into solvent extraction of rice bran oil and its physical refining. The plant has the capacity to process 3.5 tons/hour of rice bran and refine 2.5 tons/hour of rice bran oil. Currently, the plant is processing around 60 tons/day of rice bran and refining about 50 tons/day rice bran oil. The industrial unit has a 15 m 3/day capacity Effluent Treatment Plant (ETP) for treating the wastewater it generates. The treated wastewater is reportedly disposed off on land for irrigation.

The existing ETP is opinioned as of under capacity unit, and the industrial unit has not been consistently complying with the applicable effluent discharge standards. In view of this, the industrial unit has approached Dr. Akepati S. Reddy, TCIRD, Thapar Technology Campus, Patiala for critically look into the existing ETP for its capacity and adequacy to handle the wastewater currently being generated and comply with the applicable effluent discharge standards. Consequent to the request, Dr. Reddy has visited the industrial unit and its ETP on 30-09-2009.

The existing ETP is in fact under-designed. While the wastewater generation is >40 m3/day, capacity of the ETP is just 15 m3/day. Further, while the ETP is designed to treat the wastewater with 50 mg/L of oil and grease, 250 mg/L of BOD and 500 mg/L of COD, the wastewater to be treated has 0.2% (2000 mg/L) oil and grease, 2000-8000 mg/L COD and 400-1600 mg/L BOD5 at 20C. In view of this, and in view of many other design defects of the existing ETP, Dr. Reddy has opinioned to go for a new and higher capacity ETP that can successfully handle the higher strength wastewater currently generated by the industrial unit. This feasibility report is consequence this. This report comprehensively looks into the wastewaters being generated by the industrial unit, proposes a few important in-plant wastewater minimization and control measures and an appropriate scheme for the wastewater treatment. Further the report includes design details of different treatment units that constitute the proposed ETP.

2. Industrial processes and wastewaters generation

The industrial plant actually includes a rice bran oil solvent extraction unit and a rice bran physical refining unit. The proposed effluent treatment plant (ETP) is supposed to handle and manage the wastewater generated by both the industrial units.

2.1 Rice Bran Oil Solvent Extraction Unit

The solvent extraction process includes the following steps:

Demoisturizing

Cooking

Palletizing

Pellet cooling

Solvent extraction

Pellet desolventing

Distillation recovery of the solvent

Stripping

2.1.1 Demoisturizing: It is a continuous process. Here, the rice bran is heated in a steam jacketed vessel with baffles for about 10 minutes for driving out the internal moisture. Use of steam (40 PSI) in the jacket results in the generation of condensate. This condensate is currently collected, conveyed and used in the boiler as boiler feed water.

2.1.2 Cooking: Demoisturized rice bran is loaded into the bran cooker (a horizontal tube with a screw pushing the bran through the tube). 20 PSI steam is applied directly on the moving bran for facilitating cooking and surface moistening.

2.1.3 Palletizing: Cooked and moistened bran is loaded into pellet machines and forced to pass through a screen with the help heavy rollers. The rollers are driven by a geared electrical drive. Gear oil of the pellet machine is cooled by circulating cooling water in the cooling water coil.

2.1.4 Pellet cooling: Hot bran pellets are conveyed over a screen for about 70 feet distance for the cooling. In the first 20 feet path the pellets are cooled by sucking cool air through the pellets over a conveyor screen with the help of blowers. In the next 50 feet path, the pellets are cooled by blowing cool air over them with the help of fans. After cooling the pellets with about 10% moisture are conveyed into solvent extractors.

2.1.5 Solvent extraction: Solvent extraction is a 5-stage batch counter-current process. 3.5 tons of pellets, taken in the extractor, are sprayed with solvent (hexane) at the top.

The sprayed solvent is allowed to drain through the packed column of pellets and collected at the bottom sump. From here, the solvent is pumped and reused for the spraying. This process of solvent extraction is continued for about 3 hours in each stage. In the first stage, fresh pellets are extracted by the oil rich solvent taken from the 2 nd stage of extraction. Then the pellets are moved to the 2nd stage of extraction, while the solvent is collected into a tank (rich extract tank-1). In the 5th stage, the pellets are finally extracted with fresh solvent, and then, while the solvent is moved to the 2nd stage, the pellets are subjected to desolventing.

2.1.6 Pellet desolventizing: The pellets are steamed with 100 PSI steam for about 30 minutes for driving out the residual solvent as vapours. About 1.5 tons of steam is used for this purpose. Because of the steaming, the bran pellets accumulate moisture to the 25% level. Exhaust steam, together with the solvent vapours, is condensed in a surface condenser, wherein circulating cooling water acts as a sink for the heat generated from the condensation. Condensed solvent together with the steam condensate is drained into a vertical vessel for facilitating layer separation of the water from the solvent. Non-condensable gases are taken out with the help of a vacuum pump.

2.1.7 Distillation recovery of the solvent: Oil rich solvent obtained from the extractor (and solvent contaminated with oil) is distilled, in a heater, with steam, in coil. Steam consumption in the distillation column is about one ton per hour. The steam condensate generated here is collected and conveyed to the boiler house for reuse as boiler feed water. Vapours of the distillation unit are condensed in a surface condenser by circulating cooling water and taken into a vertical vessel for the layer separation of water and solvent. Non-condensable gases are handled by the vacuum pump. Residual oil left in the distillation unit is then passed on to the stripping column for the removal of traces of solvent.

2.1.8 Steam Stripping: Oil from the distillation unit is made solvent free through steam stripping at 120C in a steam jacketed stripping column. Condensate generated from the use of steam in the jacket is collected and conveyed to the boiler for reuse as boiler feed water. Vapours of the stripper column are condensed in a surface condenser with circulating cooling water and taken into a vertical vessel for the layer separation of water and solvent. Non-condensable gases are handled by the vacuum pump.

2.1.9 Vacuum pumps: There are two vacuum pumps for taking care of the non-condensable gases accumulating in the surface condensers of the solvent extraction unit. These pumps put together are run for about 12 hours a day and use about 1 m3/hour of fresh cool groundwater as sealing water. The sealing water, during use, get contaminated with the condensed vapours of the surface condensers. The used sealing water is collected into a 12 m3 capacity vertical tank for layer separation of water and solvent. The water

layer is drained out at regular intervals as wastewater, and the solvent layer is taken into the heater for the distillation recovery of solvent.

2.1.10 Cooling tower and circulating cooling water system: Circulating cooling water is supplied, at the 1200 lpm rate, with the help of four pumps, and circulated through all the surface condensers of the solvent extraction unit for condensing the vapours. The cooling water in circulation is apparently getting contaminated with the used vacuum pump sealing water. Further, the foul condensate generated in the solvent extraction unit is also used as makeup water in this circulating cooling water system. No conditioning chemicals are added to the circulating cooling water. Cooling tower blow-down is not practiced. When felt sufficiently contaminated, the circulating cooling water is completely drained out (once in 45 days) and replaced with fresh water. Capacity of the sump of the cooling tower is 130 m3 (6.6 m x 6.5 m x 3 m).

Process and material flow details of the solvent extraction process are shown in the following figure:

2.2 Rice Bran Oil Physical Refining Unit

Physical refining of the rice bran oil includes the following steps:

1. Degumming/neutralization

2. Bleaching

3. Single dewaxing

4. Deodourizing

5. Double dewaxing

2.2.1 Degumming/neutralization: It is batch process carried out in a 12 m3 capacity heating vessel with steam coil heating and stirring provisions. Bran oil taken in the vessel is first heated to about 50C and dosed with phosphoric acid at the rate of 3 kg/m3. After dosing the acid, the oil is further heated to 70-80C and maintained there for about one hour and then added with about 500 L water. Contents of the heating vessel are then heated and maintained at 80-90C for another four hours and then transferred into a bleaching vessel for bleaching. 2 kg/cm2 pressure steam is used in the steam coil for the heating and the steam condensate generated is drained out as wastewater. Quantity of the steam condensate generated is insignificant and most of it is lost as flashed steam.

2.2.2 Bleaching: It is also a batch process carried out under vacuum conditions. The bleaching vessel has steam coil and connected to a vacuum system of direct contact condenser for facilitating heating of the contents and for creating the necessary vacuum respectively. The vacuum system is assisted by a vacuum pump, specially, for taking care of the non-condensable gases. Degummed oil transferred into the bleaching vessel has 0.8 to 0.9% moisture. Through heating the oil and activating the vacuum system, desired level of vacuum is created in the vessel. After this, bleach earth (at 3% rate) and activated carbon powder (at 0.8% rate) are dosed into the vessel and the contents are mixed for about 40 minutes for brining about the bleaching.

2.2.2.1 After the bleaching, oil of the bleaching vessel is passed through filter press for taking out the used bleaching earth and activated carbon in the form of filter cake. The filtered oil is then sent to the dewaxing unit. The filter cake generated at the filter press has around 22% oil. The filter fabric used in the press is cleaned usually monthly once by dipping in 1 m3 of hot 2.5% caustic solution for about an hour. Each fabric, after dipping in caustic solution is then rinsed, first in 1 m3 water, taken in a vessel, and then manually through application of water sprays/jet. Caustic level in the cleaning vessel is maintained through addition of makeup caustic and hot water. The rinse vessel is dumped and filled with fresh water when it becomes dirty (usually after rinsing about 20 fabrics).

2.2.3 Dewaxing: Bleached oil after filtering is taken into a crystallizer for the crystallization removal of the wax present in it (2.5%). In the crystallizer, the oil is gradually cooled from around 70C to around 20-23C over 24 hour period through circulating first cooling water and then chilled water. The chilled water required is supplied by an ammonia chiller plant. Around 95% of the wax present in the oil is crystallized. After crystallization, the oil is filtered through filter press for the removal of the wax crystals. The wax cake removed at the filter press has 65% oil and 35% wax. For the recovery of additional oil, the cake is first heated to about 200C, then cooled to around 11C and then pressed in a hydraulic press. This reduces the oil content of the wax cake to half. The fabric used in the filter press is cleaned in hot (100C) dewaxed oil. The dewaxed oil is then sent to the deodourizing unit.

2.2.4 Deodourizing: Deodourizing unit is run a maximum of 4 days a week. Dewaxed oil is taken into feed tanks and from there pumped through spira flow heat exchanger and deaerator for the removal of any dissolved gases. The oil (in the spiraflow heat exchanger) is heated to around 100-120C with thermic fluid prior to its entry into the deaerator. In the deaerator, the oil is further heated to around 150C with thermic fluid for the deaeration to occur. Vapours and gases generated at the deaerator are handled by a vapour condensation system comprising of a direct contact condenser.

2.2.4.1 Deaerated oil is then pumped through a VHF, a packed column and a deodourizer for removing the fatty acids and deodourizing the oil. In the VHF, the oil is further heated to 240C by thermic fluid (in the jacket and heating coils) and steam stripped through using direct steam of 12-13 kg/cm2 pressure. In the packed tower, the oil is sprayed at the top and passing down the column while 12-13 kg/cm2 pressure steam is passed from the bottom counter-current to the oil for the steam stripping of the fatty acids. In the deodourizing unit, the oil, while being heated with thermic fluid in coil, is again steam stripped for further removal of fatty acids.

2.2.4.2 Fatty acid vapours and gases emanating from the VHF, the packed column and the deodourizer are collected into a receiver and condensed through

direct injection of the cooled fatty acid condensate (sometimes after cooling in an external plate heat exchanger with circulating cooling water)

indirect cooling of the receiver tank contents with circulating cooling water

use of a direct contact condenser

The non-condensable gases are taken care of by an associated steam ejector and vacuum pump.

2.2.4.3 Fatty acid condensate accumulating in the receiver tank is maintained at a specified level through draining out the excess of fatty acid as byproduct. Water soluble fatty acids and the steam used (in the deaerator, VHF, packed column, and deodourizer) ultimately become part of the cooling water, in circulation between the cooling tower and the direct contact condensers. Instead of using fresh water, the output water of the direct contact condensers is collected, cooled in a cooling tower and reused as cooling water in the direct contact condensers. There is a separate cooling tower and circulating cooling water system for supplying the cooling water for the indirect cooling of the receiver tank contents.

2.2.5 Double dewaxing: Single dewaxing is reported to remove only 95% of the wax originally present in the oil. Double dewaxing is practiced for the removal of the rest of residual wax of the oil. Deodourized oil is taken into a buffer tank, passed through an oil cooler and then taken for the double dewaxing. Procedure followed for the double dewaxing is very similar to that of single dewaxing, but the crystallization of the wax is carried out at relatively lower temperature (around 11C). After the crystallization, the oil with wax crystals is filtered through filter presses for the removal of the wax crystals in the form of wax cake.

2.2.6 Cooling towers and circulating cooling water systems: There are three cooling towers and circulating cooling water systems (the first one for cooling the compressed ammonia, the second one for supplying cooling water for indirect cooling, and the third one for supplying cooling water to the direct contact condensers) associated with the bran oil physical refining plant. Of these, the circulating cooling water system supplying water to the direct contact condensers is contaminated with water soluble and water insoluble fatty acids. Further, volume of the cooling water in circulation gradually increases overtime, from the condensation of the steam used for stripping. For facilitating the retaining and removal of the floating fatty acid contamination, the cooling water, after use, is passed under baffle walls prior to pumping to the cooling tower, for cooling and reuse. Sumps associated with the cooling towers are quite big (8mx8mx6m, 8mx4mx6m and 8mx8mx6m respcetively). Circulating cooling water of the system associated with direct contact condensers is dumped once in 45 days and replaced by fresh water. In the other two cases the circulating cooling water is dumped only once in a season.

2.2.7 Ammonia chiller: It is used for supplying chilled water to the dewaxing unit (wax crystallizer). There are two ice banks wherein chilled water is prepared (by vapourizing and passing liquid ammonia through coils) and stored. From the ice banks chilled water is pumped, circulated through the crystallizer and taken back to the ice bank. Ammonia vapours, after compressing, are passed through overhead heat exchanger tubes for cooling and the cool liquid ammonia is taken back into a receiver tank and reused in chilled water

production. Cooling water sprays are applied on the heat exchanger tubes for facilitating the cooling of liquid ammonia.

Process and material flow of the physical refining unit is schematically shown in the following figure:

2.3 Supporting Facilities

2.3.1 Water supply system: Both ground water and canal water are used in the plant. through a open drain the canal water is conveyed to the plant premises and stored in a water tank and from there the water is pumped and distributed for use.

2.3.2 Soft water plant: Ion-exchange resin based soft water plant is used for the production of soft water from the canal water and supply to the boiler. The plant included no pressure sand filter and no activated carbon column. The ion-exchange resin bed is found getting clogging much before it is exhausted. After every 2.5 to 3 hours run, it required regeneration. Regeneration has been reported to generate about 1.5 m3/cycle of regeneration wastewater.

2.3.3 RO water plant: RO water plant has been used to produce RO water from the ground water and supply to the boiler. Reject stream of the RO plant is wasted as wastewater. Reject to accept stream ratio is 1:1. RO water generation rate is 4 kL/hour.

2.3.4 Boiler: 10 ton/hour capacity rice husk fired boiler is used to supply steam to both solvent extraction and rice bran oil refining units. The boiler is usually run at 8-9 ton/hour capacity. About 12 m3/day steam condensate is collected, in the solvent extraction unit, and returned to the boiler for reuse as boiler feed water. In addition to this, soft water (produced by the soft water plant from the canal water) and RO water (produced by the RO water plant from the ground water) are also used as the boiler feed water. The boiler generates boiler blow-down water (wastewater!).

3. Inventory of the wastewaters generated

3.1 Rice bran oil solvent extraction unit

Wastewater streams Characteristics and quantities

Foul condensate from pellet desolventing

Steam consumption in the pellet desolventing unit is 1.5 tons per batch. Of this about 0.5 tons is left in the pellets as moisture. Net foul condensate generation rate here is estimated at <42 m3/day.

Foul condensate from the steam stripping unit

Less than 0.5 tons/hour of steam is used directly in the stripper for the stripping. The foul condensate generation rate here is estimated at <12 m3/day.

Sealing water of vacuum pumps associated with the surface condensers for handling non-condensable gases

Sealing water consumption rate is 1 m3/hour and the two vacuum pumps together are run for about 12 hours a day. The sealing water generation rate here is 12 m3/day.

Dumped water from the circulating cooling water and cooling tower system of the solvent extraction unit

Capacity of the sump associated with the cooling tower is 130 m3. Assuming replacement of the circulating cooling water with fresh water once in every 45 days, the wastewater generation rate can be estimated at <3.0 m3 per day.

3.2 Rice bran oil physical refining unit

Wastewater streams Characteristics and quantities

Wastewater from the cleaning of the fabric of the filter press

Generated monthly once over 3 or 4 days period from the cleaning of about 100 fabrics. 2.5% hot caustic solution is used in the cleaning process. The wastewater generated is estimated at 10 m3 per month (0.35 m3/day).

Steam condensate contaminated specially with water soluble fatty acids drained out from the vapours receiving column

The wastewater generated depends on the quantity of steam used in the VHF, packed column and deodourizer. At around 60C, to which the vapours are cooled, the contaminated steam condensate generation is estimated at <3 m3/day.

Steam condensate generated at the degumming/neutralization unit

Quantity generated is insignificant and most of it is lost as flashed steam.

Steam condensate generated at the bleaching unit

Quantity generated is insignificant and most of it is lost as flashed steam.

Blow down water of the cooling tower associated with the direct contact condensers of the deodourizing unit

Cooling tower sump capacity is 384 m3 and the circulating cooling water is dumped once in 45 days and replaced by fresh water. From this, the blowdown water generation rate is estimated at 8.5 m3/day.

Blow down water from the cooling tower associated with indirect cooling in the deodourizing unit

Cooling tower sump capacity is 192 m3 and the circulating cooling water is dumped only once a season and replaced by fresh water. From this, the blowdown water generation rate is estimated at 2.13 m3/day. No conditioning chemicals are added to the water and the water is not much polluted.

Blow down water from the cooling tower associated with the compressed ammonia cooling

Cooling tower sump capacity is 384 m3 and the circulating cooling water is dumped only once a season and replaced by fresh water. From this, the blowdown water generation rate is estimated at 4.25 m3/day. No conditioning chemicals are added to the water and the water is not much polluted.

3.3 Supporting facilities

Wastewater streams Characteristics and quantities

Regeneration wastewater from the soft water plant

Water consumption in the regeneration is reported as about 1.5 m3 per regeneration. From this, the regeneration wastewater generation rate can be taken as 1.5 m3/regeneration cycle.

Reject stream of the RO water plant The RO water plant capacity is 4 m3/hour and the plant is reportedly operated at 50% rejects level. The RO water is reportedly produced only when the canal water is not available for the soft water production. While in operation, the RO water plant produces 4m3/hour of rejected water.

Boiler blow down water Boiler blow-down is reported as 4% of the steam generated. Assuming the boiler operation at 9 tons/hour capacity, the boiler blow-down wastewater generation rate is estimated at <9 m3/day. Significant portion of the boiler blow-down is reportedly lost as flash steam.

4. Waste minimization measures

4.1 Flash the boiler blow down water and recover the flashed steam into the boiler feed water tank. After flashing, use the boiler blow down water as makeup water in the cooling tower associated with the direct contact condensers of the deodourizing unit.

4.2 Work for increasing the RO water recovery from the current 50% to > 60%. Collect the RO reject water and use it as sealing water in the vacuum pumps associated with the surface condensers of the solvent extraction unit. All the reject water may not be needed by the vacuum pumps. Additional reject water, if any, may be used in the toilets in place of fresh water.

4.3 Reuse the foul condensate generated in the solvent extraction unit, at the pellet desolventing and at the steam stripping units, as makeup water in the cooling tower of the solvent extraction unit.

4.4 Steam condensate generated at the distillation heater of the solvent extraction unit may be flashed, and the flashed steam may be used as low pressure steam in the bran cooker. The condensate, together with that generated at the demoisturizer and at the steam stripper, may then be supplied to the boiler for reuse as boiler feed water.

4.5 Cleaning of the fabric of the filter press used in the degumming and bleaching can follow the following approach for minimizing the wastewater generation: To the existing rinse tank a second rinse tank may be added. Freshwater may be used only in the second rinse tank and overflows of this tank may be taken into the first rinse tank. Overflows of the first rinse tank may be collected and used in the hot caustic solution tank as makeup water, and additional overflows may be drained out as wastewater.

4.6 A pressure sand filter may be added ahead of the ion exchange resin bed of the soft water plant for avoiding clogging the resin bed and facilitating use of the resin bed to its full ion-exchnage capacity (production of at least 15 m3 of soft water per regeneration).

4.7 Practice daily blow-down of the cooling towers (rather than total dumping the cooling water at regular intervals) may be at the following rates:

Cooling tower of the solvent extraction unit: 3 m3/day

Cooling tower associated with the direct contact condensers of the deodourizing unit: 8.5 m3/day

Cooling tower associated with the ammonia chiller: 4.25 m3/day

Cooling tower associated with the indirect cooling in the deodourizing unit: 2.13 m3/day

5. Effluent treatment plant

5.1 Wastewaters needing the treatment and the treatment needed

Wastewaters to be treated in the effluent treatment plant include the following:

1. Foul condensate generated at the desolventing, steam stripping and distillation units of the solvent extraction unit: An estimated 54 m3/day foul condensate will be generated. Of this, on an average, about 38 m3/day will be used as makeup water in the cooling tower of the solvent extraction unit. Rest of the foul condensate (on an average, 16 m3/day) will be drained out as wastewater into the effluent treatment plant for treatment.

2. Blow down water of the cooling tower of the solvent extraction unit: Average cooling tower blow down water is estimated at 3 m3/day.

3. Sealing water of vacuum pumps associated with the surface condensers of the solvent extraction unit (for handling the non-condensable gases): volume of this wastewater is < 12 m3/day.

4. Wastewater generated from the cleaning of the fabric of the filter press: Volume of this wastewater will be about 0.35 m3/day but generated over 3 to 4 days period of the month.

5. Steam condensate contaminated specially with water soluble fatty acids supposed to be drained out from the vapours receiving column of the deodourizing unit: Volume of this wastewater will be about 3 m3/day. It will be generated only when the deodourizing unit is in operation (supposed to be in operation on an average 3 or 4 days a week).

6. Blow down water of the cooling tower associated with the direct contact condensers of the deodourizing unit: This water will be about 8.5 m3/day.

Total quantity of wastewater needing treatment will be about 43 m3/day. To be on safer side, for taking care of the variations in the wastewater generation rates, a 50 m3/day capacity ETP will be designed. The wastewater to be treated in the ETP is supposed to have the following composition:

S.No. Parameter Value

1. Temperature 50C

2. pH around 7.5

3. Oil and grease 0.2%

4. BOD5 at 20C 400 -1600 mg/L

5. COD 200 – 8000 mg/L

6. TSS 100 – 200 mg/L

Treated effluent coming out from the ETP will be mixed with the following relatively less polluted wastewaters and disposed off on land for irrigation (using karnal technology):

1. Blow down water from the cooling tower associated with indirect cooling in the deodourizing unit

2. Blow down water from the cooling tower associated with the ammonia chiller

3. Regeneration wastewater of the soft water plant associated with the boiler

The treated effluent after mixing with the above wastewaters are believed to have the following quality:

S.No. Parameter Value

1. pH Around 7.5

2. Oil and grease < 10 mg/L

4. BOD5 at 20C < 100 mg/L

5. COD < 250 mg/L

6. TSS < 100 mg/L

5.2 Scheme of treatment proposed for the wastewater

The treatment is supposed to achieve the following:

Reduction of the oil and grease from 0.2% level to <10 mg/L level

Reduction of the BOD5 at 20C from 400-1600 mg/L level to <100 mg/L level

Reduction of COD from 2000-8000 mg/L level to <250 mg/L level

Reduction of TSS from 100-200 mg/L level to <100 mg/L level

For this, an Effluent Treatment Plant (ETP) comprising of the following treatment units is proposed:

Oil and suspended solids removal unit

Upflow anaerobic reactor

Sequencing Batch Reactor (SBR)

The oil and suspended solids removal unit is supposed to remove most of the floating oil and the settleable suspended solids. The upflow anaerobic reactor is supposed to take of the COD/BOD and transform the relatively high strength wastewater into medium to low strength wastewater. The resultant medium to low strength wastewater is treated in the Sequencing Batch Reactor (SBR), for meeting the limits prescribed for BOD, COD and even for TSS. SBR has been chosen here mainly because of the smaller volumes of the wastewater to be treated (50 m3/day).

For handling the sludges generated by the ETP during the wastewater treatment, a sludge pit and a filter press and associated facilities are included in the ETP. For facilitating collection of the wastewaters generated, and their pumping and passing through the ETP, a raw effluent sump, pumps and necessary piping are also included in the ETP. Similarly, for facilitating mixing of the treated effluent with the least polluted wastewater streams of the industrial unit, and for facilitating regulator’s sampling of the treated effluent, a treated effluent sump with overflow provision is also included in the ETP.

All the wastewaters to be treated are collected into the underground raw effluents sump and from there pumped by one of the two raw wastewater pumps and loaded to the oil and suspended solids removal unit. In this unit, conditions suitable for the floating removal of oil and for the settling removal of suspended solids are maintained. Outlet of the unit is designed to retain the floating oil back. Enough space is allocated in the unit for storing the settled solids and the floating oil. At regular intervals (15 or 30 days once), the accumulated floating oil is manually removed and disposed off separately (can be sold to the soap manufacturing units). The settled sludge of the unit is also drained out at

regular intervals and handled along with the sludge drained out from the upflow anaerobic reactor and from the SBR.

Effluent of the oil and suspended solids removal unit is allowed to flow under gravity to the bottom of the upflow anaerobic reactor and forced to flow upwards through the reactor. This is supposed to bring better contact between the active anaerobic sludge blanket (accumulated in the reactor) and the wastewater to be treated and ensure higher rates of anaerobic oxidation of organic matter. Accumulation of the active anaerobic sludge regulated through draining out part of the sludge at 15 days interval. Effluent of the upflow anaerobic reactor is collected with the help of a sub-surface drain and allowed to flow under gravity into the SBR.

In the SBR the organic matter is aerobically biooxidized through maintaining active aerobic microbial biomass and supplying the air/oxygen required with the help of a diffused aeration system comprising of fine bubble membrane diffusers, two blowers and necessary piping and fittings. After aerating for about 8-9 hours, the aeration is stopped and inflow of wastewater is stopped, and the SBR contents are allowed to settle for about 2-3 hours. After the settling, the supernatant is drained out from the SBR into the treated effluent sump as treated effluent. After this, inflow of wastewater is allowed and diffused aeration is started for the next cycle of treatment. Sludge accumulation in the SBR is regulated through draining out desired amount of the sludge may be weekly once.

Sludge drained out from the oil and suspended solids removal unit, from the upflow anaerobic reactor and from the SBR are collected into the sludge pit. From there it is pumped by a screw pump and loaded to the filter press for dewatering. If needed flocculating agents are added to the sludge for improving the dewatering properties of the sludge. Filtrate generated at the filter press is allowed to flow under gravity into the raw effluent sump. The dewatered sludge generated at the filter press is dried under the sun and disposed off (can be applied on land as soil conditioner).

5.3 Design details of the facilities associated with the proposed ETP

The proposed ETP will include the following facilities:

1. Raw effluent sump

2. Two raw wastewater pumps

3. Oil and suspended solids removal unit

4. Upflow anaerobic reactor

5. Sequencing batch reactor

6. Diffused aeration system comprising of two blowers, 9 diffusers and necessary piping and fittings

7. Treated effluent sump

8. Sludge pit

9. Sludge pump and press filter

5.3.1 Raw effluent sump and pumps: The raw effluent sump will be an underground tank for receiving the wastewaters needing treatment. Effluent storage capacity of this sump will be 10 m3 and its dimensions will be 2.5 m length, 2.5 m width and 1.6 m depth (from the invert level of the wastewater inlets). There will be two non-clog self-priming pumps (one in operation and one standby) for pumping raw wastewater from the raw effluent sump into the oil and suspended solids removal unit. The pumps will be of 30 m3/hour pumping capacity and >10 m head.

5.3.2 Oil and suspended solids removal unit: This unit will have ability to retain the floating oil and the settlable solids that can possibly be loaded over one month period. This will be an above ground tank and its wastewater retention time will be 24 hours. Dimensions of this tank are 8 m length, 4 m width, 2 m liquid depth and 0.5 m free board. Inlet of this tank includes a trough of 0.3 m depth and 0.2 m width running along the width. It will have multitude of lateral orifices of 0.1 m depth and 0.2 m width at the bottom for discharging the wastewater into the oil and suspended solids removal unit. Outlet of this unit includes a baffle upto 0.2 m below the liquid level and 0.5 m above the water level, a 4.0 m long overflow weir and a clarified effluent collection trough of 0.2 m width, 0.2 m liquid depth and 0.5 m free board. For details please the figure below:

5.3.3 Upflow anaerobic reactor: This reactor can be partially above ground and partially below ground. Dimensions of this reactor will be 5 m length, 3 m width, 4 m liquid depth and >0.5 m free board. Bottom of this reactor will have 1:3 widthwise slope towards middle. Clarified and oil free wastewater coming from the oil and suspended solids removal unit will be delivered at 0.3 m height from the bottom at central line of the reactor with the help of two 100 mm internal diameter PVC distribution pipes. A distribution box will be used for the equal distribution of the wastewater between the two distribution tubes. At the liquid subsurface, 3 PVC pipes of 6 inch internal diameter with slit openings and cap will be used to collect the treated effluent and convey into the next treatment unit, SBR. Provision will be made for draining out excess sludge, if required, from the bottom of the reactor. For details see the above figure.

5.3.4 Sequencing batch reactor: This reactor can also be partially above ground and partially below ground. Dimensions of this reactor will be 3 m length, 3 m width, 4 m liquid depth and 0.5 m free board. Effluent collected at the subsurface of the upflow anaerobic reactor is taken into this reactor through an inlet which has valves for preventing wastewater flow if desired. 9 fine bubble membrane disc diffusers, each with the ability to deliver 5 Nm3/hour of air will be provided at 0.3 m height from the bottom of the tank for aerating the tank contents. 2 route blowers (one in operation and one

standby) each of 45 Nm3/hour air delivery capacity at 0.55 to 0.6 kg/cm2 pressure will be provided for supplying the compressed air required. Provisions will be made to the tank for draining the clear supernatant from above the settled sludge layer. Similarly, provision is also made for draining out the sludge from the bottom of the SBR.

5.3.5 Sludge pit and Filter press: Settled sludge of the oil and suspended solids removal unit, the upflow anaerobic reactor and of the Sequencing Batch Reactor (SBR) will be collected into this pit. That is, all the three sludge drain pipes open into this pit. The sludge pit will have about 7.5 m3 sludge storage capacity and its dimensions will be 2.5 m length, 2 m width, 1.5 m depth below the invert level of the sludge drain and > 0.5 m free board. From here with the help of a screw pump the sludge will be lifted and loaded to a filter press for dewatering. The filter press will have the capacity to handle 7.5 m3 of sludge per day. An open drain will be provided between the filter press and the raw effluent sump for carrying the filtrate, generated at the filter press, into the raw effluent sump.

5.3.6 Treated effluent pit: This pit will receive the supernatant drained out from the SBR. Its effluent holding capacity will be 10 m3 and its dimensions will be 2.5 m length, 2.5 m width, 1.6 m liquid depth and sufficient freeboard. This pit will also be receiving the low strength wastewater for mixing with the treated effluent. This pit will have a provision for the overflow of the treated effluent into a drain that conveys the effluent to the site of disposal on land for irrigation.

Layout for the ETP can be as shown in the following figure:

5.4 Hydraulic design of the ETP

Facility details Level with respect to datum

Bottom of the raw effluent sump 1.6 m below the invert level of the lowest incoming wastewater drain

Bottom of the inlet trough of the oil and suspended solids removal unit (OSSRU)

0.20 m below the liquid level of the OSSRU (datum)

Bottom of the outlet trough of the oil and suspended solids removal unit

0.20 m below the liquid level of the OSSRU

Drop provided in the distribution box on the inlet of the upflow anaerobic reactor

0.20 m

Liquid level in the upflow anaerobic reactor

0.40 m below the liquid level of the OSSRU

Bottom of the effluent trough of the upflow anaerobic reactor

0.60 m below the liquid level of the OSSRU

Liquid level in the SBR 0.70 m below the liquid level of the OSSRU

Supernatant drain of the SBR 1.5 m above the bottom of the SBR

Invert levels of the sludge drains opening into the sludge pit

1.25 m below the liquid level of the OSSRU