Treatment of Laboratory Wastewater by Sequence Batch Reactor Technology.
Summary: These studies were conducted on the characterization and treatment of sewage mixed with waste -water of research and testing laboratory (PCSIR Laboratories Lahore). In this study all the parameters COD, BOD and TSS etc of influent (untreated waste-water) and effluent (treated waste-water) were characterized using the standard methods of examination for water and waste- water. All the results of the analyzed waste-water parameters were above the National Environmental Quality Standards (NEQS) set at National level. Treatment of waste-water was carried out by conventional sequencing batch reactor technique (SBR) using aeration and settling technique in the same treatment reactor at laboratory scale. The results of COD after treatment were reduced from (90-95 %), BOD (95-97 %) and TSS (96-99 %) and the reclaimed effluent quality was suitable for gardening purposes.
Pollution of water by organic and inorganic chemicals is of serious environmental concern [1, 2]. As global economy expands rapidly development of new industries exerts more and more pressure on environment in relation to the disposal of waste- water after proper treatment.
Waste-water is a complex mixture of natural inorganic materials mixed with man made substances, including material washed from roads, roofs, kitchens. It is a complex mixture that ends up at the waste-water treatment plant for purification. In its broadest sense waste-water can be split into domestic waste-water also known as sewage, industrial waste-waters and finally, municipal waste- water which is a mixture of the two. It is generally cheaper for waste-water producer to treat its own waste-water prior to its disposal to the local sewer to reduce the treatment costs [3-6]. The strength and composition of waste-water changes on an hourly, daily and seasonal basis, with average strength dependent on per capita water usage, infiltration, surface run off as well as local habits and diet . Sewage is 99.9 % water with the material that requires being removed amount to just 0.1 % by volume.
This solid material consists of a mixture of faces, food particles, greases, oils, soaps, salts, metals, detergents, solvents, dyes, and other chemicals, sand and grit. Grit is composed of proteins, carbohydrates and fats, salts etc. The aim of this mixed waste-water treatment is to convert this solid portion to a manageable sludge (2 % dry) while leaving effluent (0.003 % dry solids) [8, 9] and to use this treated waste-water for gardening purpose and reduce the pressure on local water resources. Sewage treatment is the process of removing contaminants from waste-water by physical, chemical, and biological means. Its objective is to produce a waste stream and a solid waste suitable for discharge or reuse back into the environment. This material is often inadvertently contaminated with many toxic organic and inorganic compounds. It can be treated near to where it is created or collected and transported via a network of pipes and pump stations to a municipal treatment plant.
Sewage collection and treatment is typically subject to local regulations and standards. Industrial sources of waste-water often require specialized treatment process .The sewage treatment involves three stages called primary, secondary and tertiary treatment first; the solids are separated from the waste-water stream. Then dissolved biological matter is progressively converted into solid mass by using indigenous, water borne microorganisms. Finally, the biological solids are neutralized then disposed off or reused and the treated water may be disinfected chemically or physically.
The water used for different purposes such as laboratory, washing, bathing, gardening/ agricultural uses, consumption is estimated to be one hundred thousand gallons daily and the waste-water generated is approximately 40 thousand gallons. The composition of PCSIR laboratories Lahore wastewater consist of residential, black water from toilets, gray water from bath, kitchen's waste-water generated from the research and development activities of PCSIR laboratories complex is disposed of combined with sewer without any treatment. The objective of this study is to treat the combined waste- water and make it safe and fit for disposal into the local sewer/ waste-water body. The final effluent can be discharged into a stream, river, lagoon it can be used for the irrigation of green way or park. If it is sufficiently clean. It can also be used for ground water recharge.
Results and Discussion
In this study 44 grab and composite samples were collected initial 11 samples were collected on monthly basis to assess the pollution load on the mixed waste-water of PCSIR laboratories complex Lahore. One monthly grab and composite sample contains four grab and composite samples. One weakly sample consists of 24 hours sampling. The next other 33 samples were characterized after using different treatment options. In these 33 samples first 11 samples were aerated for a fixed time at a constant speed without any separation of solid material but the biological oxygen demand (BOD) was not reduced as required in the National Environmental Quality Standards fixed by the Environmental Protection Agency. Sample results were 100 % out of EPA limits. In second treatment the sludge was separated and oxidation was done for a fixed time at a constant speed, four samples (36.3 %) were in the limits of EPA and 7 samples (63.4 %) were out of limit of National Environmental Quality Standards (NEQS).
In the third phase of biological treatment combined with air oxidation using organisms present in the waste-water after sedimentation all the 11 samples (100 %) characterized for biological oxygen demand (BOD) Parameter were in the limits of National Environmental Quality Standards (NEQS) and were suitable for disposal into the local water bodies.
After first treatment option 100 % (11) samples were out of EPA limits, after second treatment 4 out of 11 were within the limits of EPA but after the third treatment 11 out of 11 (100 %) were within the EPA limits for chemical oxygen demand (COD) parameter.
In appearance of raw waste-water sample was dirty color. The fermentation and degradation occurred due to enormous qualities of bacteria and colloids completely devoid of dissolved oxygen. All the results of chemical analysis are above the National Environmental Quality Standards (NEQS) fixed by the ministry of Environment, Government of Pakistan. The Standards are given in Table.No-1. The results of characterization of raw effluents are given Fig no. 1-5 and Fig no.6 and 7. After primary and secondary treatment to influent waste-water was colorless, transparent, odor free. All the compounds in the waste-water were broken down into stable inorganic and organic compounds. Dissolved oxygen was present in effluent with concentrations 1 to 2 mg/L, which is in compliance with NEQS. BOD5, COD values before and after sedimentation and biological treatment are given in graph 7 and 8.
Removal of biological oxygen demand (BOD) in primary sedimentation is 40-50 % and secondary sedimentation 90-95 % this removal of BOD is comparable with NEQS. The BOD and COD removal before and after sedimentation shows 95 % removal efficiency with respect to NEQS given in Table.no.1 [10, 11].
Table-1: National environmental quality standards.
Sr. # Parameter###NEQS Limit
1.###pH at 25oC###6-10
3.###BOD5 at 20oC###80mg/L
The grab and composite samples of waste- water were collected from the main disposal point of the PCSIR laboratories complex to the local drain. The samples were collected in a range of 8 to 200 liters. Temperature, pH, conductivity, turbidity and DO were measured at the site. A small size sample of two litters was taken off separately from the bulk sample in a plastic bottle placed in icebox for the COD, BOD, and other parameters. The methods used for the chemical analysis of waste-water were standard methods for the examination of water and waste-water . The results of samples are presented in the graphs of 1-4 and 6-7. During this study the samples were treated for the reduction of Chemical Oxygen Demand (COD), biological oxygen demand (BOD) and total suspended solids (TSS). The organic content of waste-water is traditionally measured using lumped parameters such as BOD, COD [13-15].
Sample Handling and Preservation for BOD5
Sample was collected in 1 liter plastic container and preserved immediately in refrigerator for analysis at 20 degC.
Reagents and Chemicals
Distilled water was used for making sample dilutions:
Aqueous Solution of Starch as Indicator
Standard sodium thiosulphate titrant 6.205 gm Na2 S2 O3-5H2O in distilled water was dissolved and 1.5 mL 6 N, NaOH solution was added and then diluted to 1000 mL. Standardized with potassium iodate.
Procedure for BOD5
BOD bottle was filled with BOD water and 1 mL of phosphate buffer was added, MgSO4, CaCl2, and FeCl3 solutions was added in water. Seed dilution water, water was saturated with dissolve oxygen. Before using, the dilution water temperature was brought to 20 + 3 degC.
Determination of Initial DO
The sample contains materials that react rapidly with DO, initial DO was determined by membrane electrode immediately after filling BOD bottle with diluted samples.
Dilution Water Blank
Dilution water was used as blank rough check on quality of unseeded dilution water and cleanliness of incubation bottles. Together with each batch of samples, a bottle of unseeded dilution water was incubated. The DO uptake was 0.2 mg/L.
Sample was incubated at 20 degC + 1degC BOD bottles containing dilutions covered with aluminum foil, seed controls, dilution water blanks, and glucose glutamic acid checks.
Determination of Final DO
After 5 days incubation DO was determined in dilution blank sample. To a 300 mL bottle, 1 mL MnSO4 solution was added, followed by 1 mL alkali- iodide - azide, reagent stopper was carefully closed to exclude air bubbles and mix by inverting bottle a few times. Then 1 mL conc. H2SO4 was added and titrated a volume corresponding to 200 mL original samples after correction of sample loss by displacement with reagents. Sample was titrated with 0.025 M Na2S2O3 solution to a pale straw color. Few drops of starch solution were added and continue to titration till first disappearance of blue color .
For titration of 200 mL of sample, 1 mL 0.025 Na2S2O3 = 1 mg DO/L. For each test bottle meeting the 2.0 mg/L minimum DO depletion and the 1.0 mg/L residual DO, calculate BOD5 as follows:
BOD5, mg/L = D1 - D2
D1=DO of diluted samples immediately after preparation, mg/L.
D2=DO of diluted sample after 5 d incubation 20 degC, mg/L.
P=Decimal volumetric fraction of sample used.
Sample Handling and Preservation for COD
Samples were tested without delay. All samples were homogenized before analysis.
Sample was homogenized and then pipetted out 50 mL into a 500 mL refluxing flask. Smaller portion was diluted to 50 mL. 1 g mercuric sulphate was added, several glass beads were also added, and 5mL sulphuric acid was added very slowly, with mixing to dissolve mercuric sulphate. Sample was cooled while mixing to avoid possible loss of volatile materials.
25 mL 0.04167 M potassium dichromate solution was added and mixed. Flask was attached to condenser and turned on the cooling water. Remaining sulphuric acid (70 mL) was added through open end of condenser continue stir erring and mixing while adding sulphuric acid.
Open end of condenser was covered with a small beaker to prevent foreign material from entering refluxing mixture and was refluxed for 2 hours. After cooling the condenser was washed with distilled water. Reflux condenser was disconnected and mixture was diluted to about twice its volume with distilled water. After cooling to room temperature solution was titrated to excess potassium dichromate with FAS, using 2 to 3 drops ferroin indicator. End point of the titration was taken as the first sharp color change from blue green to reddish brown that persists for 1 minute. Duplicate determinations were agreed within 5 % of their average. A blank sample containing the reagents and a volume of distilled water equal to that of sample in the same manner was refluxed and titrated. Standard potassium hydrogen phthalate solution was evaluated .
COD as mg O2/L = (A-B) x M x 8000/mL sample where:
FAS = Ferrous Ammonium Sulphate
A = mL FAS used for blank
B = mL FAS used for sample
M = molarity of FAS and
8000 = milliequivalent weight of oxygen x 1000 mL/L.
The Sequence batch Reactor process the Air is given to the mixed liquor for several hours in the reactor and then clarified liquid is obtained. But in the process in which the laboratory waste-water (mixed) was treated without using any external biomass and chemicals the waste-water taken in the quantities varying from 8 liters to 180 liters. In first step the settling was done for 1/2 hour then sludge and liquid was separated in another reactor and aeration was done at a constant speed for a various time intervals using a air compressor fixed with a Rota meter. After different time intervals the liquid was taken off characterized for COD and BOD.SBR process is a fill and draw type reactor that acts as aeration basin and final clarifier. Waste-water was mixed with air and allowed to react over several hours in the presence of air. At a certain point, the aeration is turned off and mixed liquor in the reactor is allowed to settle, after a short settling period, the clarified treated effluent is discharged.
Once the treated effluent is discharged the reactor is available to treat a further batch of waste-water. In this way, the process operates on a batch treatment principle, with the operations being sequenced within 3 to 4 hours. Two or more Sequence Batch Reactor (SBR) may be operated in parallel batch system [14-16]. Process is described in the Fig. 8.
Further research work is needed for optimization of different aspects of treatment processes.
Discharge of oxygen demanding materials present in the municipal and industrial waste-waters has resulted in the depletion of the dissolved oxygen levels in the receiving waters during low flow periods especially in the vicinity of large urban and industrial centers, thus seriously affecting the ecological balance of the surface waters. The direct use of raw sewage for irrigation purposes should be discouraged due to health risks. Reuse of waste-water for irrigation purpose after adequate treatment needs to be promoted. This can supplement irrigation water in addition to providing nutrients for plant growth and reducing surface water pollution. To safeguard the environment and protect public health from the harmful effects of the pollutants proper control measures in terms of engineering solution and legislative measures are needed to be undertaken.
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1Center for Environmental Protection Studies, PCSIR Laboratories Complex, Lahore, Pakistan.
2Applied Chemistry Research Centre, PCSIR Laboratories Complex, Lahore, Pakistan.
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|Author:||Imtiaz, Naz; Butt, Muhammad Tahir; Saeed, Rauf Ahmad Khan Muhammad Tariq; Irfan, Muhammad|
|Publication:||Journal of the Chemical Society of Pakistan|
|Date:||Dec 31, 2012|
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