Sanjeev Chaudhari

ANAEROBIC DECOLORISATION OF SIMULATED TEXTILE WASTEWATER CONTAINING AZO DYES

This study deals with the decolorization of the commercially important azo dyes, Orange II (C.I. Acid Orange 7) and Reactive Black 3HN (C.I. Reactive Black 8) under anaerobic conditions in wastewater. Laboratory scale semicontinuous studies were conducted using simulated cotton dyeing wastewater at ambient temperatures (24-28 degrees C) by maintaining a HRT of 10 days. The dye concentration in wastewater was maintained at 100 mg/l. The reactors were operated for 58 days and Orange II and Black 3HN were easily decolorized under the experimental conditions employed. The performance of the bioreactors was evaluated by monitoring oxidation-reduction potential (ORP) in the reactor, color and Chemical oxygen demand (COD) removal. Color removal of >99% was achieved in both the dye-containing reactors. COD removals of up to 95%, 92% and 94% were achieved in control, orange- and black dye-containing reactors, respectively. Effect of dyes and salts present in textile wastewater on methanogenesis was evaluated based on maximum methane production and methanogenic activity. Based on the maximum methane production data, no inhibition of methanogenesis was observed for dye concentrations of up to 400 mg/l for both the dyes. However from the methanogenic activity data, it was observed that the black dye concentration of 400 mg/l seemed to cause inhibition of methanogenesis.

Effects of water chemistry on arsenic removal from drinking water by electrocoagulation

Exposure to arsenic through drinking water poses a threat to human health. Electrocoagulation is a water treatment technology that involves electrolytic oxidation of anode materials and in-situ generation of coagulant. The electrochemical generation of coagulant is an alternative to using chemical coagulants, and the process can also oxidize As(III) to As(V). Batch electrocoagulation experiments were performed in the laboratory using iron electrodes. The experiments quantified the effects of pH, initial arsenic concentration and oxidation state, and concentrations of dissolved phosphate, silica and sulfate on the rate and extent of arsenic removal. The iron generated during electrocoagulation precipitated as lepidocrocite (γ-FeOOH), except when dissolved silica was present, and arsenic was removed by adsorption to the lepidocrocite. Arsenic removal was slower at higher pH. When solutions initially contained As(III), a portion of the As(III) was oxidized to As(V) during electrocoagulation. As(V) removal was faster than As(III) removal. The presence of 1 and 4 mg/L phosphate inhibited arsenic removal, while the presence of 5 and 20 mg/L silica or 10 and 50 mg/L sulfate had no significant effect on arsenic removal. For most conditions examined in this study, over 99.9% arsenic removal efficiency was achieved. Electrocoagulation was also highly effective at removing arsenic from drinking water in field trials conducted in a village in Eastern India. By using operation times long enough to produce sufficient iron oxide for removal of both phosphate and arsenate, the performance of the systems in field trials was not inhibited by high phosphate concentrations.

Heavy metal–Soluble starch xanthate interactions in aqueous environments

The effectiveness of the water-soluble starch xanthate (SSX) process for removal of heavy metals [Hg(II), Cu(II), Cd(II) and Ni(II)] has been evaluated. Removal of Hg(II) and Cu(II) is effective; Cd(II) and Ni(II), less so. The metal [Hg(II)/Cu(II)] binding capacity remains the same in the pH range 3–7. An optimum metal/SSX ratio is observed for maximum metal removal. The metal removal efficiency of SSX appears to be dependent on a specific chemical interaction between metal and SSX and on separation of the metal–xanthate complex from the aqueous phase. An analogy between the metal–SSX system and the colloid–cationic polyelectrolyte system (coagulation and flocculation in water treatment) is observed. The role of ionic strength for metal–SSX system appears to be analogous to the role of indifferent electrolyte in coagulation and flocculation.

Evaluation of Natural Coagulants for Direct Filtration

In the present study surjana (Moringa oleifera) seed, maize (Zea mays) and chitosan were used in direct filtration of Bilaoli lake water and evaluated for their efficiency in removing turbidity and microorganisms from water. The experiments with these natural coagulants gave filtered water turbidity less than or almost equal to 1NTU and thereby met the turbidity criteria for drinking water as per WHO guidelines. Bilaoli lake water had low ionic strength and low turbidity which represents one of the most difficult raw waters to treat, but natural coagulants in direct filtration achieved good filtrate quality. The head loss development across the filter bed with chitosan was more than that of alum, while with maize it was comparable to that of alum. With M. oleifera seeds the head loss was much less in comparison to alum. The average most probable number (MPN) reductions obtained with M. oleifera seeds, maize and chitosan were 97.35%, 95.4% and 87.1% respectively, whereas, with alum it was only 7.7%.

Evaluation of soluble and insoluble xanthate process for the removal of heavy metals from wastewaters

Abstract The effectiveness of xanthate (water soluble and water insoluble) process for hexavalent chromium removal has been evaluated. Insoluble xanthates were synthesized in the laboratory from corn starch (ICSX), potato starch (IPSX) and cellulose powder (ICX), and their removal efficiency for Cr(VI) is compared with soluble starch xanthate (SSX). In preliminary experiments various insoluble xanthates were tested for their effectiveness in removal of both metallic cation [Cd(II)] and metallic anion (chromate). The results indicated that the metal binding capacity followed the sequence q e ( ICSX ) > q e ( IPSX ) ⋍ q e ( ICX ) . Comparison between ICSX and SSX revealed that ICSX has better removal capacity for Cr(VI) on unit weight basis. However, based on chemical requirements for the synthesis of ICSX and SSX, SSX appears to be better than ICSX. The removal of Cr(VI) decreased with increase in pH while ionic composition of the aqueous phase had little effect on the removal for both soluble and insoluble xanthates. The removal mechanism for Cr(VI) appears to be reduction and complexation of the reduced chromium with xanthate groups. A comparative analysis of the traditional reduction-precipitation process and xanthate process for hypothetical waste containing hexavalent chromium revealed that xanthate process would be a worthwhile alternative.

Bioaccumulation and biosorption of drimarene red dye by Aspergillus foetidus

An isolated fungus, Aspergillus foetidus, was found to uptake azo reactive dye(s) such as drimarene red under active growth and growth unsupportive conditions. Microscopy indicates preferential accumulation of drimarene red dye in the tips of fungal hyphae. The presence of 0.1% azide and phosphate in the fungal growth medium causes displacement of bound dye from the biomass. The key factors that influence the process of biosorption of dye in growth non-supportive medium are pH, temperature, and age and concentration of fungal biomass. Based on the Langmuir isotherm plots, the maximum fungal biosorption capacity (Qo value) was computed to be 344 mg g-1 using the fungal spent medium at pH 2.5 and 60°C. Sodium hydroxide is an effective agent for the leaching of dye from the loaded fungal biomass. The results suggest the possibility of applying the isolated fungus for decolourisation of textile mill wastewater.

Treatment of Petrochemical Wastewater by Rotating Biological Contactor

A laboratory scale study has been conducted to assess the efficiency of rotating biological contactor (RBC) to treat the synthetic wastewater from a petrochemical industry producing acrylonitrile. The attached biomass was acclimatised by gradually increasing cyanide concentration from 5 to 40 mg l−1 with simultaneous increase in the concentration of chemical oxygen demand (COD) and ammonium nitrogen (NH4 +-N). During acclimatization COD removal varied between 80-88 percent (%) while cyanide removal was more than 99%. The RBC was operated at varying hydraulic loading rates from 0.011 to 0.027 m3 m−2 d−1. The performance of the RBC was monitored for various parameters like COD, 5-day biochemical oxygen demand at 20-degree centigrade (°C) [BOD5], cyanide, ammonium nitrogen etc., for all hydraulic loadings. At all hydraulic loadings the cyanide removal remained more than 99%. The removals obtained in terms of percentage, for cyanide, COD, BOD5 and NH4 +-N were greater than (>) 99, 95.2, 99.1 and 77, respectively at hydraulic loading of 0.011 m3 m−2 d−1. The effect of substrate/cyanide ratio on the performance of the process at five different ratios, 100/1, 80/1, 60/1, 40/1 and 20/1, showed more than 99% cyanide removal at ratio 20/1. The effect of COD/nitrogen (N) ratio was studied at four different ratios, 12/1, 10/1, 8/1 and 6/1, showed cyanide removal remained unaffected. The variation of biomass concentration within the system was also studied.

Laboratory evaluation of a water-treatment sequence using Moringa oleifera seed coagulant

A water extract of Moringa. oleifera seed was applied to a treatment sequence comprising coagulation-flocculation-sedimentation-sand filtration. Model waters (kaolinite suspensions) of turbidities 10, 100, 300 and 700 NTU were prepared. For the 10 NTU water, the optimum dose was only evident when sand filtration was incorporated into the treatment sequence. For the higher water turbidities tested, a relatively broad optimum dose range exists post filtration. After filter ripening, the filtrate turbidities obtained for the 300 and 700 NTU raw water turbidities were 1 NTU and 3 NTU respectively. Headloss development was gradual giving relatively long filter runs.

A Cost-Effective Technology for Arsenic Removal: Case Study of Zerovalent Iron-Based IIT Bombay Arsenic Filter in West Bengal

Arsenic is present in groundwater in some parts of India. Despite the fact that a variety of treatment methods are available, the efficiency of these methods is not fully known. With the revision of Indian standards for permissible levels of arsenic in drinking water to 10 μg/L or lower, it is necessary to develop a treatment method, which meets drinking water standards of 10 μg/L. Iron based adsorbents have been reported to have high affinity for arsenic. Many researchers have also shown that the corrosion of Zero Valent Iron (ZVI) forms Hydrous Ferric Oxide (HFO) which can act as an adsorbent for arsenic. And the oxidation of Fe to Fe has also been reported to oxidize As(III) to As(V). Using this information a ZVI based Arsenic Filter has been developed by Indian Institute of Technology, Bombay. Test units of the IITB-Arsenic Filter have been installed in the field in four villages in West Bengal. From the results, it is clear that the filter is able to consistently achieve arsenic levels around 10 μg/L for initial arsenic concentrations ranging from 0.06 to 0.4 mg/L. The flowrate of the filtered water is aprox. 600 L/hr. Thereby the IITB-Arsenic Filter is able to consistently provide drinking water for about 200 families on a daily basis. The IITB-Arsenic Filter does not require frequent backwashing/cleaning (cleaning frequency is once in 3 months, and is done by the villagers) and therefore has low operation and maintenance costs. Moreover, it does not require monitoring of flow parameters and is easy-to-operate by unskilled personnel. The Fe/As ratio used in the filter is around 20. Low Fe/As ratios mean lesser sludge generation. Thus it is felt that the IITB Arsenic filter is a suitable technology for rural India.

Effect of reactor configuration on performance during anaerobic treatment of low strength wastewater.

The efficiency of the up-flow anaerobic sludge blanket (UASB) reactor is quite low for the treatment of low strength wastewaters (LSWs) due to less biogas production leading to poor mixing. LSW may be treated efficiently by providing adequate mixing in the UASB reactor when gas production is low, and sufficient mixing can be achieved by modifying reactor geometry. Hence, modifying UASB reactor geometry for enhanced mixing and evaluating its performance for the treatment of LSWs would be a worthwhile effort. In the present study, UASB reactor configuration was modified by providing a vertical baffle along the height to promote mixing of reactor contents, and is termed as modified UASB (MUASB). The performance of an on-site pilot-scale MUASB reactor was evaluated for 375 days under ambient condition for the treatment of municipal sewage as LSW and compared with that of the conventional UASB and hybrid UASB (HUASB) reactors. The MUASB reactor showed better performance in terms of chemical oxygen demand (COD) removal efficiency as compared with UASB and HUASB reactors during this study. At 4 h hydraulic retention time, the total COD removal efficiency of UASB and HUASB reactors was 53.7% and 61%, respectively, which were much lower than the total COD removal efficiency of the MUASB reactor (72.7%). The better performance observed in the MUASB reactor is possibly due to improved mixing. Depth-wise analysis of reactor liquid showed that better mixing in the MUASB reactor enhances the contact of wastewater with biomass, which contributes to the improved treatment efficiency. It seems that MUASB holds promise for LSW treatment.