DESC:FIELD OF THE DISCLOSURE:
The present disclosure relates to an industrial wastewater treatment. The present disclosure, particularly relates to a process of wastewater treatment for continuous and simultaneous removal of COD and turbidity from the wastewater via bio-filtration.
Definitions:
Chemical oxygen demand (COD) is a measure of the total quantity of oxygen required to oxidize all the organic material into carbon dioxide, ammonia and water.
Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at a certain temperature over a specific time period.
The BOD value is most commonly expressed in milligrams of oxygen consumed per liter of sample during 5 days of incubation at 20°C and is often used as a robust surrogate of the degree of organic pollution of water.
BACKGROUND:
The treatment of wastewater is a complex field as the concentration and identity of the contaminated materials to be treated are constantly changing. Additionally, the flow rate, pH, oxidation potential, concentration of solids and temperature of the wastewater, among other factors, are also variable. Further, wastewater contains organic matter such as colloids, dissolved ionic matter, dissolved non-ionic matter, surfactants, and suspended solids. Such contaminated materials are present in combination with similar types of inorganic materials. Industrial wastewater produced during industrial processing has proven to be difficult to treat due to the many different types of contaminants present therein. Filtration systems using different types of filters have found wide use in the treatment of wastewater. A common problem with such systems is the frequent need to clean or replace the filters due to fouling and clogging.
Bio-filtration is a process that uses a bacterial mass attached onto the filter media as a biofilm to oxidize much of the organics to carbon dioxide and water and utilize as a carbon source for their own proliferation and growth. Thus, the process is self-sustaining and self-regenerating. Bio-filters have been successfully used with vapor systems, e.g. odour control and treatment of volatile organic compounds, but its commercial use in liquid system is emerging.
The US granted patent number 5403487 suggests a process for aerobically degrading an industrial wastewater feed containing toxins for microorganisms. The process involves (a) inoculating a fixed packed bed of pieces of macro porous synthetic resin bio-support having micro pores with an inoculum of a culture acclimated to aerobically degrade said toxin; (b) flowing, in the presence of a molecular oxygen-containing gas, the feed essentially free of solids, over and around the pieces of bio-support, through said fixed bed for the microorganisms in said inoculum to replicate, and incrementally increasing flow of the feed until essentially all pores of the resin have lodged therein; (c) maintaining a pH within a range from 6.0 to 8.5; and (e) recovering a purified feed containing less than 10 ppm of said toxin.
The US granted patent number 6100081 mentions an apparatus for the purification of wastewater and/or waste gas using a biofilter containing a filtering material, wherein the wastewater moves downwardly there into, while the waste gas moves upwardly or downwardly there into. It also discloses a filtering composition comprising filtering carrier material which is composed of wood shavings & peat.
The granted German patent number 69329547 mentions a biofilter for treating contaminated air. It uses immobilized biofilm on filter support media to biodegrade the sorbed volatile organic compounds (VOCs) and bio transform inorganic oxides of sulfur (SOx) and nitrogen (NOx) to residuals such as carbon dioxide, water and various acids.
The Japanese patent application number 200310329 mentions a biological treatment means comprising a plurality of means for treating wastewater containing various organic substances by using microorganisms. It consists of a turbidity meter for measuring the turbidity of a solid-liquid separation means, concentration meters for measuring the concentration of nitrous acid and nitric acid in an aeration tank, an aeration means capable of controlling aeration volume in the aeration tank and a nitrification inhibitor adding means for adding a nitrification inhibitor to the aeration tank.
The US granted patent number 6811702 suggests a process and installation for treating a polluted aqueous liquid having a COD value caused by organic compounds present therein and a BOD/COD ratio smaller than 0.2. To reduce the COD value, the polluted aqueous liquid is percolated through a packed filter bed of activated carbon, which is colonized with aerobic bacteria and which forms an adsorbent for at least a part of said organic compounds. To provide a thin, fully aerated biofilm of bacteria on the carrier material so that no oxygen has to be dissolved under pressure in the liquid, the filter bed is kept at the most partially submerged position in the liquid percolating there through. The percolate which has passed through the filter bed is collected and a portion of the collected percolate is re-circulated to the filter bed whilst a further portion of the collected percolate is removed as treated effluent by means of a membrane filter.
The US granted patent number 7258793 mentions a method and an apparatus for treating an organic liquid waste with a biofilm in which the organic liquid waste is dissolved with oxygen under a first pressure higher than atmospheric pressure to prepare a pressurized oxygen-dissolved organic liquid waste. The pressurized oxygen-dissolved organic liquid waste is depressurized to prepare a depressurized oxygen-dissolved organic liquid waste. The depressurized oxygen-dissolved organic liquid waste is contacted with the biofilm to prepare a treated organic liquid waste.
The US granted patent number 7374683 suggests a biofilter for the purification of waste liquid using layers of filtering material, wherein the waste liquid moves downwardly by gravity while an O2-containing gas moves upwardly therein. The biofilter comprises a gas collector to capture at least a portion of the gas moving upwardly therein to mitigate the problem of biofilter clogging due to a microbial seal at the surface of the uppermost filtering layer.
The US granted patent number 7887706 mentions a method for bio-filtration of a liquid effluent by simultaneous nitrification and denitrification which uses the addition of an oxygen source at a predetermined rate and optionally the addition of a carbon source (such as whey) thus enabling the complete transformation of the nitrates (NO3) present in the effluent at the time of treatment through a biofilter. The specific operating conditions favoring the simultaneous nitrification and denitrification include the controlled injection of a slight quantity of air, adjustment of the level of nitrogen load (TKN+NO3) and the level of carbon load thereby making possible elimination, for most part of the release of the unwanted nitrogen in the form of NO3 or NO2.
The US patent application number 20090078639 suggests a filter medium which comprises a mass of elongate, differently orientated, shape-sustaining elements comprising a sponge material. The different orientation of the elements forms a self-supporting open network which provides substantial interstitial space between the elements.
Durgananda Singh Chaudhary et al in the paper, ‘Granular Activated Carbon (GAC) Biofilter for Low Strength Wastewater Treatment’ disclose use of a GAC (Granular activated carbon) biofilter for treating wastewater. However, the process of the paper is best applicable for low strength wastewater. Further, the efficiency of the waste removal process has been found to be about 55%. Even further, the time period taken by the process described in the paper has been around 30 days. Still further, optimum efficiency has been achieved at steady state conditions.
Cheerawit Rattanapan et al in the paper, ‘Removal of H2S in down-flow GAC bio-filtration using sulfide oxidizing bacteria from concentrated latex wastewater’ describe a bio-filtration system for the removal of H2S by means of sulfur oxidizing bacteria, immobilized on GAC. The time period for achieving H2S scavenging is found to be about 3 days.
Though several methods and bio-filters for treating wastewater have been mentioned in the prior art published documents, none discuss the reduction of the organic content and turbidity in a simultaneous manner. Also, most of the prior art methods are time consuming. A need is, therefore, felt for developing a cost effective and efficient process for treating wastewater via bio-filtration.
Furthermore, considering the generation of a large amount of wastewater from the petroleum and petrochemical plants, there is a significant amount of interest in the reuse of water from the petroleum and petrochemical facilities. It is envisaged that the wastewater after the treatment i.e. after the removal of dissolved and suspended solid matters can be re-utilized in the petroleum and petrochemical plants as a solution to their water needs such as a source of cooling water.
Accordingly, there is a need in the art to provide an efficient process for continuous and simultaneous reduction of chemical oxygen demand and turbidity from the wastewater particularly generated in petrochemical and the polymer plants.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies are as follows:
It is an object of the present disclosure to provide a process for simultaneous reduction of chemical oxygen demand (COD) and turbidity from a wastewater.
It is another object of the present disclosure to provide a process for reduction of chemical oxygen demand (COD) from wastewater having high pH value.
It is yet another object of the present disclosure to provide a process for reduction of turbidity from wastewater having high pH value
It is still another object of the present disclosure to provide a process for reduction of chemical oxygen demand (COD) and turbidity from wastewater which is having poor biodegradability.
It is yet another object of the present disclosure to provide a process that requires less time for reduction of chemical oxygen demand (COD) and turbidity from a wastewater.
Other objects and advantages of the present disclosure will be more apparent from the following description and drawings which are not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure provides a process for treatment of wastewater having a pH ranging from 6 to 10, a COD ranging from 100 ppm to 1000 ppm, a turbidity ranging from 50 NTU to 500 NTU and a ratio of BOD/COD less than 0.6, the process comprising:
a) allowing at least a portion of the wastewater to settle for removal of coarse suspended particles;
b) aerating the wastewater to obtain an aerated stream;
c) adding nutrients to the aerated stream to support the growth of a biomass;
d) allowing the biomass to acclimatize and settle to obtain an active biomass comprising consortium of micro-organisms;
e) separating the active biomass from the wastewater;
f) supporting the active biomass on granulated activated carbon (GAC) to form a GAC supported bio-film; and
g) passing a portion of the wastewater through the GAC supported bio-film to obtain a bio-filtered water having COD ranging from 5 ppm to 200 ppm and turbidity ranging from 2 NTU to 75 NTU.
Typically, the wastewater is a petrochemical wastewater or a PVC wastewater.
Typically, the nutrient is at least one selected from a group consisting of nitrogen, phosphorous, yeast extract, minerals and vitamins, and a proportion of nutrients ranges from 0.5 mg to 2.5 mg with respect to 100 ppm of COD.
Typically, the microorganism is an “aerobic” bacteria, and is at least one selected from a group consisting of Pimelobacter simplex, Bacillus cereus, Micrococcus sp, Bacillus sp, Serratia sp, Sphingomonas sp, Psuedomonas sp, Microbacteriaceae bacterium, Kocuria sp and Aeromicrobium sp.
Typically, the bio-filtered water contains contaminants having a particle size less than 25 microns.
In accordance with the present disclosure, the COD in the bio-filtered water is reduced by 75% to 85% and the turbidity in the bio-filtered water is reduced by 85% to 95%, as compared to the wastewater.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The disclosure will now be described with reference to the accompanying non-limiting drawings:
Fig. 1 illustrates a schematic diagram of a bio-filtration system (100) for treatment of a wastewater in accordance with the present disclosure;
Fig. 2a illustrates the effect of flow rate on COD removal in accordance with the present disclosure;
Fig. 2b illustrates the effect of flow rate on turbidity removal in accordance with the present disclosure;
Fig. 3a illustrates the effect of pH on the extent of COD removal in accordance with the present disclosure;
Fig. 3b illustrates the effect of pH on the extent of turbidity removal in accordance with the present disclosure;
Fig. 3c illustrates the extent of COD removal at high severity operation in accordance with the present disclosure; and
Fig. 3d illustrates the extent of turbidity removal at high severity operation in accordance with the present disclosure.
DETAILED DESCRIPTION
The present disclosure provides a process for treatment of wastewater and the process also precludes the drawbacks associated with the conventional wastewater treatment processes.
It is known that wastewater from petrochemical and/ or polymer industries is generated in a large amount and its COD (chemical oxygen demand) typically ranges between 100 and 1000 ppm whereas, the turbidity ranges between 50 and 500 NTU. Moreover, the BOD/COD ratio of these waters is less than 0.3, indicating poor biodegradability. Accordingly, it is desirable to treat such wastewater to reduce COD and turbidity simultaneously in order to re-use the wastewater for various purposes such as cooling operations.
The present disclosure have focused on the aforesaid problems and have found an efficient process which can reduce COD and turbidity of the wastewater such as wastewater from polyvinyl chloride (PVC) manufacturing plant in a continuous manner without requiring two systems for removing COD and turbidity separately.
In accordance with the present disclosure, a process for treatment of wastewater having a pH ranging from 6 to 10, a COD ranging from 100 ppm to 1000 ppm, a turbidity ranging from 50 NTU to 500 NTU and a ratio of BOD/COD less than 0.6, the process comprising of:
a) allowing at least a portion of the wastewater to settle for removal of coarse suspended particles;
b) aerating the wastewater to obtain an aerated stream;
c) adding nutrients to the aerated stream to support the growth of a biomass;
d) allowing the biomass to acclimatize and settle to obtain an active biomass comprising consortium of micro-organisms;
e) separating the active biomass from the wastewater;
f) supporting the active biomass on granulated activated carbon (GAC) to form a GAC supported bio-film;
g) passing at least a portion of the wastewater through the GAC supported bio-film to obtain bio-filtered water.
In accordance with the present disclosure, the GAC supported bio-film obtained in step (f) is called as “bio-filter”.
Typically, the wastewater is having a ratio of BOD/COD less than 0.3.
In accordance with the present disclosure, the pH of the wastewater is in the range of 6.5 to 9.5.
In accordance with the present disclosure, the step (b) is carried out for a time period ranging from 10 minutes to 60 minutes.
Typically, the nutrient is at least one selected from a group consisting of nitrogen, phosphorous, yeast extract, minerals and vitamins and a proportion of nutrients ranges from 0.5 mg to 2.5 mg with respect to 100 ppm of COD.
In accordance with the present disclosure, the biomass is acclimatized to obtain the active biomass for use as biofilm in the GAC supported biofilter.
Typically, the microorganism is an “aerobic” bacteria, and is at least one selected from a group consisting of Pimelobacter simplex, Bacillus cereus, Micrococcu sp, Bacillus sp, Serratia sp, Sphingomonas sp, Psuedomonas sp, Microbacteriaceae bacterium, Kocuria sp and Aeromicrobium sp.
In accordance with the present disclosure, the step (f) is carried out at a temperature ranging from 200C (ambient temperature) to 500C for a time period ranging from 2 hours to 4 hours.
Typically, the bio-filtered water contains contaminants having average particle size of 10 microns.
Typically, the COD and the turbidity in the bio-filtered water are reduced by 75% to 85% and 85% to 95% respectively, as compared to the wastewater.
The process utilizes the GAC (granulated activated carbon) supported biofilm developed from an acclimatized microbial consortium originating from activated sludge of ETP (effluent treatment plant) of petrochemical industries or polymer industries.
During the contact of the wastewater with the GAC supported biofilm, the microorganisms of the biofilm degrade the organic matter and the activated carbon causes the adsorption of the non-dissolved particulate contaminants. Therefore, upon passing the wastewater through the GAC supported biofilm, the wastewater is subjected to degradation, adsorption and filtration, resulting in bio-filtered water ready for downstream use.
Fig.1 illustrates a schematic diagram of a bio-filtration system (100) for treatment of wastewater in accordance with the present disclosure. The bio-filtration system (100) comprising:
i. at least one feed tank (T);
ii. at least one pump (P);
iii. at least one bio-filtration column (C); and
iv. at least one effluent collection pot (ECP).
The feed tank (T) of bio-filtration the system (100) holds the settled wastewater and supplies the same to the bio-filtration column (C) via the pump (P). The (P) pressurizes the incoming wastewater and directs the pressurized stream to the bio-filtration column (C). The bio-filtration column (C) receives the pressurized wastewater and causes the dissolved and non-dissolved contaminants in the wastewater to be removed by means of the GAC supported biofilm present in the column. The bio-filtered water is then directed to an effluent collection pot (ECP) which stores the bio-filtered water for further use.
In accordance with one embodiment of the present disclosure, the bio-filtration system (100) comprise at least one valve (V) adapted to regulate the flow of the streams passing through the bio-filtration system (100).
In accordance with another embodiment of the present disclosure, the pump (P) is a peristaltic pump.
In accordance with an exemplary embodiment of the present disclosure, there is provided a process for simultaneously removing COD and turbidity of PVC wastewater. The process involves passing the PVC wastewater having COD ranging from 100 ppm to 400 ppm, turbidity ranging from 50 NTU to 300 NTU, contributed chiefly by off-grade PVC particles coated with polyvinyl acetate (PVA), of size ranging from 10 microns to 600 microns and a ratio of BOD/COD less than 0.3, through the granulated activated carbon supported biofilm.
Typically, the biofilm is an acclimatized bacterial culture medium that is developed and separated from the activated sludge generated during the effluent treatment of the PVC wastewater.
It is observed that the water obtained after the treatment meets the specifications of the cooling water make-up, for re-use within the plants, resulting in, zero effluent discharge, and savings in the discharge cost. The process of the present disclosure can also conserve an important natural resource, namely water.
In accordance with the present disclosure, the biofilm supported on GAC can sustain the shock loadings of COD, and the biofilm cultures can restore and perform successfully. The GAC support, which is a major component of the operating cost, is found to be self-regenerating and retains its mechanical as well as physical integrity.
In accordance with the present disclosure, the step (a) and the step (b) are carried out to support the growth and proliferation of the microorganisms, and to make the overall process self-sustaining and self-regenerating.
The resultant bio-filtered water having reduced content of dissolved and non-dissolved contaminants is collected. The COD of the bio-filtered water is found to be ranging from 5 ppm to 200 ppm, whereas the turbidity of the bio-filtered water is found to be ranging from 2 NTU to 75 NTU. The bio-filtered water obtained by the process of the present disclosure has specifications similar to that of make-up water and may be used as a cooling media and/or may be re-used after mild chlorination (treating with less than 2 ppm of chlorine) in the same plant.
The present disclosure is further illustrated herein below with the help of the following examples. The examples used herein are intended merely to facilitate an understanding of the ways in which the embodiments herein may be practiced and to further enable those of skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
Example 1: Process for the removal of COD and turbidity of wastewater (Lab scale)
1A] Process for the selection of microorganisms from the activated sludge source:
Activated sludge was collected from an ETP in 5L carboy. Acclimatization of the sludge containing a consortium of microorganisms in PVC wastewater for selective growth and enrichment of cultures capable of degrading the PVC wastewater was carried out. It was a 3 step process carried out for 9 days. The consortium of microorganisms contained Pimelobacter simplex, Bacillus cereus, Micrococcu sp, Bacillus sp, Serratia sp, Sphingomonas sp, Pseudomonas sp, Microbacteriaceae bacterium, Kocuria sp and Aeromicrobium sp.
The thickened sludge comprising mixed liquor suspended solids (MLSS) in the range of 3000 ppm to 3500 ppm was used. The PVC wastewater settled for half an hour was used for the acclimatization having a COD of 164 ppm and turbidity of 234 NTU. After 72 hours of first acclimatization, the COD and the turbidity reduction were 92% and 73% respectively. At the end of the second acclimatization (using a fresh feed), the COD and the turbidity reduction were 93% and 81% respectively. After the third acclimatization, the COD reduction was stabilized at 94% and the turbidity was stabilized at 97%.
Thus at the end of the third acclimatization, it was found that the COD and the turbidity removal capacity were more, hence, the cultures were ready for biofilter column preparation.
Samples of this culture were isolated on TYG media, purified and preliminarily identified as Gram positive or negative bacteria. The detailed identification was later carried out by DNA sequencing.
1B] Procedure for COD and Turbidity removal:
Reference is made to Figure 1, wherein a bio-filtration system for achieving bio-filtration of wastewater is demonstrated. At the end of the third acclimatization, the cultures were allowed to settle and the supernatant fluid was discarded. The sludge was collected together and approximately 80 ml was added to the pretreated/cleaned GAC (Granular Activated Carbon) in a beaker with just enough PVC wastewater to cover the surface of the GAC. The surface area (BET) of the GAC was around 1000 m2g-1. The beaker, covered with aluminum foil on which pin holes were made, was made to stand overnight. After about 16 hours the filter medium was filled into a bio-filtration column (C) having 56 cm length and 3.4 cm internal diameter. The column (C) contained 160 g of granular activated carbon (GAC bed height of 38 cm). The glass column was initially packed with a glass wool at the bottom.,. The GAC supported biofilm was added into the column with gentle tapping to allow proper settling. Further, a layer of pebbles (1/2 inch) was added on the top of the column. The column was allowed to settle for a couple of hours and then wastewater is pumped from the top of the column by the pump (P). The outlet tube from the bottom of the biofilter column (C) was taken up to bend near the top of the column and the wastewater was allowed to fall into the receiving vessel to maintain the liquid level in the biofilter.
The pump (P) was set at a flow rate of 2.4 ml/min at the outlet of the biofilter. A feed tank (T) contained the PVC wastewater having a COD of 350 ppm and turbidity of 200 NTU that was made to stand for 15 minutes to30 minutes and then aerated (DO = 6 ppm to 7 ppm, about 10 to12 bubbles/min), followed by addition of nutrients (Nitrogen = 8.75 mg and Phosphorus = 1.75 mg). The flow rate at the inlet of the column was set at a flow rate of approximately 2.4 ml/min. The outlet, which was at the bottom of the column was kept open in such a position that the flow rate at this point was also at 2.4 ml/min. This was periodically checked manually and also at the end of 24 hours (by checking the total amount of treated effluent collected). The pump (P) was shut for half an hour every 24 hours. Sampling of the effluent was done between 5 hours and 6 hours of operation and again after 23 hours to 24 hours for COD, turbidity, pH and dissolved oxygen (DO). This operation was carried out continuously for the whole period of study (approximately 3 months to 6 months for each set of experiments studied).
The treated effluent from the bio-filtration column outlet was collected in an effluent collection pot (ECP) and was found to have 50 ppm COD (83% removal) and turbidity of 15 NTU (92% removal).
1C] Effect of elevated pH (9.5):
When PVC wastewater having COD ranging from 115 ppm to 220 ppm, turbidity ranging from 100 NTU to 220 NTU, and a continuous pH of 9.5 was exposed to the biofilter according to the procedure provided in Example 1Bwith the addition of 5 mg of nitrogen and 1 mg of phosphorus, the treated effluent was still found to have an average COD of 30 ppm leading to a removal of about 82% and turbidity of 25 NTU (80%-85% removal).
1D] Effect of elevated temperature (40oC):
When PVC wastewater having an average COD of 170 ppm and an average turbidity of 175 NTU was exposed to the biofilter at a temperature of 40°C for almost 2 months, according to the procedure provided in Example 1B with the addition of 5 mg of nitrogen and 1 mg of phosphorus, the treated effluent was found to have an average COD of 37 ppm leading to a removal of about 78% and turbidity of 5 NTU to 10 NTU (more than 90% removal). The temperature of 40oC was maintained for 8 hours per day using a jacketed column and was kept at ambient for the remaining 16 hours.
When the experiments were conducted under ambient temperature (28°C to 32°C) conditions throughout (28°C to 32°C), the results obtained were practically the same. The treated effluent was found to have COD ranging from 5 ppm to 55 ppm (and turbidity ranging from 20 NTU to 30 NTU.
1E] Effect of different flow rates:
Various samples of the wastewater collected from the PVC manufacturing plant having COD ranging from 100 ppm to 200 ppm and turbidity ranging from 100 NTU to 250 NTU were treated with the biofilter of Example 1B, at ambient temperature with the addition of 5 mg of nitrogen and 1 mg of phosphorus as the nutrients, at different flow rates (1.6, 2.0, 2.4 and 2.8 ml/min).
The results have been illustrated in Fig. 2a and Fig.2b. It was found that COD removal was almost similar in all cases.
Table 1. illustrates the effect of flow rate on COD
Sr. No. Flow rate (ml/ min) COD (ppm) Percent removal (%)
1 1.6 5 – 35 85-90
2 2.0 25 – 35 80
3 2.4 20 – 50 70 - 90
4 2.8 5 – 50 60 - 85
The turbidity results after treatment were as follows:
Table 2. illustrates the effect of flow rate on turbidity
Sr. No. Flow rate (ml/ min) Turbidity (NTU) Percent removal (%)
1 1.6 10 -25 90
2 2.0 5 – 25 >90
3 2.4 5 – 30 85-95
4 2.8 20 – 40 80-85
From the experimental data, flow rate of 2.4 ml/min was found to be optimum.
1F] Effect of process parameters on COD and turbidity removal:
Fig. 3a illustrates the the effect of pH on the extent of COD removal in accordance with the present disclosure.
Fig. 3b illustrates the the effect of pH on the extent of turbidity removal in accordance with the present disclosure.
Fig. 3c illustrates the extent of COD removal at high severity of operation in accordance with the present disclosure.
Fig. 3d illustrates the extent of turbidity removal at high severity of operation in accordance with the present disclosure.
Process parameters under high severity conditions :
• The process is robust and works even at high severity conditions like flow rate of 2.4 ml/min, contact time of 2 hours, temperature of 40°C and continuous pH of 9.5.
Example 2: Process for the removal of COD and turbidity of wastewater (Pilot plant scale)
Up-scaling was done at the PVC plant to 12 m3/day (scale-up factor of 5200). The Biofilter pilot column had a total volume of 3.5 m3, the packed volume was 1.5 m3, residence time was 3 hours, an amount of GAC packing was 1 MT operating at atmospheric pressure and operating temperature of 30°C – 35°C with a flow rate of 0.5 m3/h. The iodine adsorption of GAC was 900 mg/g. A settling time of 15 min was allowed and nutrients (nitrogen of 5 mg and phosphorus of 1 mg) were added. Aeration was maintained. However, the dissolved oxygen (DO) in the feed never exceeded 2 ppm.
2A] COD measurement:
At the designed flow rate of 0.5 m3/hour, the inlet COD was between 150 and 200 ppm and the COD reduction of 70%-80% was achieved with 30 ppm -40 ppm of COD in the outlet.
2B] Turbidity measurement:
Turbidity in treated water was less than 5 NTU throughout the treatment.
2C] Effect of shock loading:
During shock loading of high COD (320 ppm), the treated outlet COD showed 100 ppm. The biofilter, however, could recover within 3 days when the COD level dropped back to 150 ppm to 200 ppm in the feed.
2D] Effect of shutdown period:
The biofilter was able to sustain a prolonged shutdown period of 10 days with just 1 intermittent replenishment of feed to the column. It was observed that, the biofilter reverted back to successful performance (70% – 80% removal) once the plant was restarted.
2E] GAC support:
The major component of the operating cost of the biofilter, was found to be self-regenerating and retaining its mechanical as well as physical integrity during the period of the trial. Fresh GAC had a surface area (BET analysis) of 750 m2/g, the GAC collected from different regions of the column after 8 months of operation showed 720 m2/g to 700 m2/g.
2F] Flow rates:
Designed flow rate could not be maintained, flow rates varied from 0.2 m3/hour to 1 m3/hour during the period of study. At 0.5 m3/hour the COD removal was 70% to 85%. At flow rate >0.6 m3/h, particularly 1m3/h, the COD removal was 65% to 85%.
Example 3: Treated water of the present disclosure can be used as a make-up source
The treated water obtained as a result of the bio-filtration process of the present disclosure was compared with those of the standard make up cooling water commonly used in industries. It was found that the specifications of both the samples were found to be similar. Therefore, the bio-filtered water of the present disclosure is capable of being used as make up cooling water in different plants or re-used in the same plant.
Along with the specifications of the standard make up cooling water, those of raw water, demineralized water and PVC centrate were also compared to yield the results provided in Table 3.
Table 3. illustrates the comparison of specifications of the biofilter treated water with the other type of water specifications
Sr. No. Parameter Specifications
Raw water Demineralized water Make up Cooling water PVC centrate water Biofilter treated water
1 pH 7.5-7.9 6.2-7.4 7.2-7.8 9.0-9.8 7-7.5
2 Conductivity (µS) 350 2.0 <5,000 150-200 170-210
3 Turbidity (NTU) 2 Nil No spec. 250-300 0-5
4 COD (mg/L) - - 50 95-150 0-20
5 TOCA (ppm) - - - ND 2-3
6 Total hardness (ppm) 160 - <1400 20-25 20-30
7 Calcium hardness (ppm) 75 - <600 6 4-6
8 Magnesium hardness (ppm) 85 - <800 14-18 14-20
9 Metal alkalinity (ppm) 300 - <100 40-60 35-55
10 Chloride (ppm) 70 1 max <400 20-30 30-40
11 Silica (ppm) 20 0.05 max <180 0.3-0.5 1-2
12 Sulfate (ppm) 10 - - Not performed 10-15
13 Orthophosphate (ppm) - - 7-11 0.5-1 2-3
14 Total Suspended Solids (ppm) (TSS) Nil - <20 65-105 1-2
15 Total dissolved solids (TDS) 450 max - <500 80-100 100-125
16 Total-Viable Count (TVC) - - <10,000 - 50,000-60,000
17 (Sulfate-Reducing Bacteria) SRB - - <10 - Nil

Example 4: Comparative examples
4A] Effect of pH and temperature: Removal of dissolved and non-dissolved contaminants using the shake flask method (conventional method) and the bio-filtration method (process of the present disclosure),
Removal of dissolved and non-dissolved contaminants was carried out using the shake flask method (conventional method similar to Activiated Sludge System) and the bio-filtration method (process of the present disclosure) and the influence of pH and temperature on COD and turbidity removal from PVC wastewater was compared.
(a) Effect of pH:
• with the shake flask method, 70% to 80% COD removal from wastewaters having a pH between 6.5 and 8.5 was observed, particularly pH greater than 8.5 resulted in <60% removal of COD; and
• with the bio-filtration method, at a flow rate of 1.6 ml/min and nutrient addition, as mentioned in Example 2, wastewaters having a pH between 6.5 and 9.5 were found to be treatable without any adjustment, leading to COD removal by 70-85% and turbidity removal of 85-90%.
(b) Effect of temperature:
• with the shake flask method, at a temperature of 29 °C to30°C, COD removal was 84% to91%, at 35°C COD removal was 74%-83% and at 40°C COD removal was only 37%; and
• with the bio-filtration method, the process of removal was found to work equally well at ambient temperature as well as at 40 °C, leading to COD removal of 75%-80% and turbidity removal of 80%-90% in both cases under conditions mentioned in (a).
It was, therefore, inferred that in the process of the present disclosure, adjustment of pH and temperature in a pre-determined range does not affect the removal of dissolved and non-dissolved contaminants from the wastewater.
4B] Effect on COD and turbidity removal: Removal of dissolved and non-dissolved contaminants using plain GAC column and the GAC supported biofilm column (bio-filtration method- process of the present disclosure),
• Two identical glass columns, one with just GAC, and the other having GAC supported biofilm were used for treatment of PVC wastewater with respect to COD and turbidity removal under identical conditions (flow rates, nutrient addition and pH).
(a) Effect on COD removal:
• COD removal was 80% in the case of GAC while it was 85% to 90% in the GAC supported biofilm;
• It was found that, over a period of three months the COD removal steadily reduced in the GAC column to 47%, and the flow rate was significantly reduced due to clogging;
• in case of GAC supported biofilm column, the COD removal was 82% and continued to remain in the range of 80% to 85% for 1 year of continuous operation. During this period there was only a requirement of periodic replenishment of acclimatized cultures to the column due to washout; and
• this indicated the self-sustaining & regenerative capacity of the biofilter in comparison to the conventional plain adsorption process.
(b) Effect on turbidity removal:
• in the GAC column, the initial turbidity removal was found to be 94%.
After 2 weeks of exposure to the wastewater, it reduced to 63% and after
a month it reduced to 50% and finally before the column stopped it was reduced to 43%;
• in case of the GAC supported biofilm column, the initial turbidity removal was found to be 90%, after which it gradually reduced to 67%-85%; and
• subsequently, due to the couple of backwashes, the removal of turbidity was restored to 85% and this continued for 1 year of continuous operation.
Therefore, the COD and turbidity removal was found to decrease over a period of time in the plain GAC column, whereas, in case of GAC supported biofilm, the COD and the turbidity removal does not decrease with time as the bio-filtration method was self-sustaining and self-regenerating.
TECHNICAL ADVANCEMENT AND ECONOMIC SIGNIFICANCE
The present disclosure relates to a process for treatment of wastewater, the process has several technical advancements:
• simultaneous removal of COD and turbidity from the wastewater.
• effective for bio-filtration of the wastewater having high pH value.
• effective for bio-filtration of the wastewater at a high temperature (for example, 500C).
• faster than the conventional processes.
• The bio-filtered water obtained from the process does not require additional filtration for further use.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “a”, “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired object or results.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the disclosure and the claims unless there is a statement in the specification to the contrary.
While certain embodiments of the disclosure have been described, these embodiments have been presented by way of examples only, and are not intended to limit the scope of the disclosure. Variations or modifications in the composition of this disclosure, within the scope of the disclosure, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this disclosure. ,CLAIMS:1. A process for the treatment of wastewater having a pH ranging from 6 to 10, a COD ranging from 100 ppm to 1000 ppm, a turbidity ranging from 50 NTU to 500 NTU and a ratio of BOD/COD less than 0.6, said process comprising:
a) allowing at least a portion of said wastewater to settle for removal of coarse suspended particles;
b) aerating said wastewater to obtain an aerated stream;
c) adding nutrients to said aerated stream to support the growth of a biomass;
d) allowing said biomass to acclimatize and settle to obtain an active biomass comprising a consortium of micro-organisms;
e) separating said active biomass from said wastewater;
f) supporting said active biomass on granulated activated carbon (GAC) to form a GAC supported bio-film; and
g) passing at least a portion of said wastewater through said GAC supported bio-film to obtain a bio-filtered water having COD ranging from 5 ppm to 200 ppm and turbidity ranging from 2 NTU to 75 NTU.

2. The process as claimed in claim 1, wherein said wastewater is a petrochemical wastewater.

3. The process as claimed in claim 1, wherein said wastewater is a PVC wastewater.

4. The process as claimed in claim 1, wherein said step (b) is carried out for a time period ranging from 10 minutes to 60 minutes.

5. The process as claimed in claim 1, wherein said wastewater is having a ratio of BOD/COD less than 0.3.

6. The process as claimed in claim 1, wherein said activated sludge is allowed to settle for a time period ranging from 30 minutes to 2 hours.

7. The process as claimed in claim 1, wherein the pH of said wastewater is in the range of 6.5 to 9.5.

8. The process as claimed in claim 1, wherein said nutrient is at least one selected from a group consisting of nitrogen, phosphorous, yeast extract, minerals and vitamins.

9. The process as claimed in claim 8, wherein a proportion of said nutrients ranges from 0.5 mg to 2.5 mg with respect to 100 ppm of COD.

10. The process as claimed in claim 1, wherein said microorganism is an “aerobic” bacteria.

11. The process as claimed in claim 1, wherein said micro-organism is at least one selected from a group consisting of Pimelobacter simplex, Bacillus cereus, Micrococcu sp, Bacillus sp, Serratia sp, Sphingomonas sp, Psuedomonas sp, Microbacteriaceae bacterium, Kocuria sp and Aeromicrobium sp.
12. The process as claimed in claim 1, wherein said step (f) is carried out at a temperature ranging from 200C to 500C.
13. The process as claimed in claim 1, wherein said step (f) is carried out for a time period ranging from 2 hours to 4 hours.
14. The process as claimed in claim 1, wherein said bio-filtered water contain contaminants having a particle size less than 25 microns.
15. The process as claimed in claim 1, wherein said COD in said bio-filtered water is reduced by 75% to 85% as compared to said wastewater.
16. The process as claimed in claim 1, wherein said turbidity in said bio-filtered water is reduced by 85% to 95% as compared to said wastewater.