Purnendu Bose

CRITICAL EVALUATION OF TREATMENT STRATEGIES INVOLVING ADSORPTION AND CHELATION FOR WASTEWATER CONTAINING COPPER, ZINC, AND CYANIDE

Industrial wastewater containing heavy metals and cyanide requires treatment for removal of both metals and cyanide before disposal. Conventional methods for treatment of such wastewater involve alkaline-chlorination for cyanide destruction, followed by pH adjustment for metal precipitation, and subsequent removal of precipitate by solid–liquid separation processes. However, excessive sludge production, slow metal precipitation kinetics, and inefficient metal removal due to poor settling and aggregation of metal precipitates, are major drawbacks of the above process. This has rekindled interest in alternative metal removal strategies involving metal adsorption and metal chelation. The objective of the study described in this paper is to critically evaluate treatment strategies involving some indigenous adsorbents and a low-cost chelating agent for treatment of a simulated wastewater containing copper and zinc, complexed with cyanide. Treatment strategies involving three adsorbents, sulfonated coal, biosorbent G. lucidum, and iron oxide coated sand (IOCS), and a chelating agent, insoluble agro-based starch xanthate (IAX), were tested. The evaluation procedure involved comparison of the performance of these treatment strategies with that of conventional treatment. Results indicate that treatment using the chelating agent IAX has the greatest potential as an alternative to the conventional treatment technique. The three adsorbents tested, although reported to be very effective in removing copper and zinc from pure systems, exhibit diminished metal removal capacity in the presence of cyanide, and hence are unsuitable.

Case Studies on Biological Treatment of Tannery Effluents in India

Abstract This paper presents a comparative assessment of the cost and quality of treatment of tannery wastewater in India by two common effluent treatment plants (CETPs) constructed for two tannery clusters, at Jajmau (Kanpur) and at Unnao in the state of Uttar Pradesh, India. The Jajmau plant is upflow anaerobic sludge blanket (UASB) process-based, while the Unnao plant is activated sludge process (ASP)-based. Investigations indicated that the ASP-based plant was superior in all respects. Total annualized costs, including capital and operation and maintenance costs, for the UASB and ASP plants were Rs. 4.24 million/million liters per day (MLD) and Rs. 3.36 million/MLD, respectively. Land requirements for the two CETPs were 1.4 hectares/MLD and 0.95 hectares/MLD, respectively. Moreover, the treated UASB effluent had higher biochemical and chemical oxygen demand (BOD/COD) and considerable amounts of other undesirable constituents, like chromium (Cr) and sulfide, as compared with the ASP effluent, which had lower BOD/COD and negligible concentration of sulfide and Cr. Sludge production from the UASB-based plant was also higher at 1.4 t/day/MLD, in comparison to the sludge production of 0.8 t/day/MLD for the ASP-based plant. Also, the entire sludge produced in the UASB-based plant was Cr-contaminated and, hence, hazardous, while only a small fraction of the sludge produced in the ASP-based plant was similarly contaminated. The results of this study are at variance with the conventional wisdom of the superiority of anaerobic processes for tannery waste-water treatment in tropical developing countries like India.

Autotrophic denitrification using hydrogen generated from metallic iron corrosion.

Hydrogenotrophic denitrification was demonstrated using hydrogen generated from anoxic corrosion of metallic iron. For this purpose, a mixture of hydrogenated water and nitrate solution was used as reactor feed. A semi-batch reactor with nitrate loading of 2000 mg m(-3) d(-1) and hydraulic retention time (HRT) of 50 days produced effluent with nitrate concentration of 0.27 mg N L(-1) (99% nitrate removal). A continuous flow reactor with nitrate loading of 28.9 mg m(-3) d(-1) and HRT of 15.6 days produced effluent with nitrate concentration of approximately 0.025 mg N L(-1) (95% nitrate removal). In both cases, the concentration of nitrate degradation by-products, viz., ammonia and nitrite, were below detection limits. The rate of denitrification in the reactors was controlled by hydrogen availability, and hence to operate such reactors at higher nitrate loading rates and/or lower HRT than reported in the present study, hydrogen concentration in the hydrogenated water must be significantly increased.

Effect of ozonation on some physical and chemical properties of aquatic natural organic matter

Abstract Natural Organic Matter (N0M) was isolated and extracted from a moderately-colored surface water, then fractionated using hydrophobic and ion exchangeresins into eight groups. Each was subjected to batch ozonation, and the rateof loss of ozone was measured. Then, selected fractions were analyzed forchanges in functional group content, molecular size and hydrophobicity; somewere further fractionated by size prior to functional group analysis. Fulvicacids and humic acids were the most reactive. These groups also showed thegreatest change in carboxyl group content and hydrophobicity. The results arediscussed with respect to impacts on coagulation. Although hydrophilicneutrals were of low to moderate reactivity, they showed the greatest promisefor improved coagulation following preozonation.

Degradation of RDX by various advanced oxidation processes : II. Organic by-products

Abstract This study resulted in the detection and identification of several organic by-products that were formed upon photolysis or oxidation of RDX by various advanced oxidation processes (AOPs). Photolysis of RDX by UV showed evidence of formation of two by-products, probably by the successive elimination of two equivalents of nitrous acid. These were tentatively identified as 1, 3-dinitro-1, 3, 5-triazacyclohex-5-ene and 1-nitro-1, 3, 5-triazacyclohex-3, 5,-ene . Both of these compounds were present as intermediates and disappeared upon further photolysis. Three other by-products were also detected which persisted for the entire duration of the photolysis process. These were identified by derivatization with O-pentafluorobenzyl-hydroxylamine (PFBHA) and subsequent extraction and GC/MS. Two of these were positively identified as PFBHA derivatives of formamide and urea. Oxidation of RDX by processes involving ozone also led to the detection of formamide and urea (as PFBHA derivatives) early in the oxidation process. However, these compounds disappeared with the progress of the oxidation process. Four other by-products which were detected only during degradation of RDX by oxidation processes involving ozone. Two were tentatively identified as N-hydroxy formamide and nitro formaldehyde , and the apparent molecular weights of the others were 88 and 102.

Analysis of photosynthetic activity in the most polluted stretch of river Ganga.

As a result of the increasing anthropogenic activities in the gangetic plain, Ganga water quantity as well as quality has declined over the years. A major effort to clean Ganga, named Ganga Action Plan (GAP) was instituted by the Government of India in 1984. The emphasis in GAP was on the reduction of organic load on the river through interception, diversion and treatment of wastewater reaching the river, thus maintaining the biochemical oxygen demand (BOD) and dissolved oxygen (DO) levels of river within the acceptable limits. A major criticism of GAP is that the significance of river ecology has not been addressed adequately during its conception and implementation. One of the important aspects from this perspective is the photosynthetic activity in the river Ganga. It has been postulated that photosynthetic activity plays an important role in maintaining high levels of DO in Ganga, and as a result the river can assimilate high organic loads without appreciable depletion in dissolved oxygen levels. Objective of the present study was to assess the photosynthetic activity and oxygen production rates in the river and correlate these values with various water quality parameters. Most polluted stretch of Ganga, which is known as the Kannauj-Kanpur stretch was chosen for this study. Based on the results of the study, it was concluded that despite implementation of phase I of GAP, and consequent diversion and reduction of organic loading to the river, both BOD and DO levels in the river has increased in the entire Kannauj-Kanpur stretch, except at Jajmau, where anaerobically treated effluent is discharged to the river. The nitrogen levels have also increased in the entire Kannauj-Kanpur stretch. Dissolved oxygen (DO) and alkalinity in the river water vary diurnally at all sites. Chlorophyll-a levels and oxygen production rates due to photosynthesis appear to be positively influenced by phosphate levels in the river water. Chlorophyll-a levels appear to be negatively correlated to the Ammonical and total Total Kjeldahl Nitrogen (TKN) content in the river water, suggesting the possibility of release of nutrients due to algal death and decomposition under certain circumstances.

Impact of addition of amendments on the degradation of DDT and its residues partitioned on soil

Market-grade DDT used for mosquito control and other purposes is a mixture of 4,4-DDT, 2,4-DDT and smaller amounts of 4,4-DDD, 2,4-DDD, 4,4-DDE and 4,4-DDMU. All above components (together known as DDTr) are strongly hydrophobic and hence are present in the environment predominantly in the soil/sediment phases. The persistence of DDTr and the feasibility of attenuation of DDTr concentration in soil matrix through addition of amendments is a subject of ongoing interest. The objective of this study was to compare the decline of soil-partitioned DDTr concentration through, (1) the natural attenuation process, (2) enhanced aerobic and anaerobic biodegradation processes involving addition of acclimatized seed and co-metabolites and (3) Nanoscale Zero Valent Iron (NZVI) addition. The extent of decline in soil DDTr concentration in control experiments, where biodegradation and photolysis were excluded, was around 10-15% in ∼100d. Extent of DDTr decline in natural attenuation experiments was 25-30% and 15-20% under aerobic and anaerobic conditions respectively. In enhanced biodegradation experiments, addition of acclimatized seed and/or co-metabolites did not enhance the extent of DDTr attenuation over and above the natural attenuation rates both in aerobic and anaerobic conditions. It thus appeared that biodegradation of DDTr adsorbed on soil was severely limited and controlled by desorption and consequent bioavailability of DDTr in the aqueous phase. In case of NZVI addition, the rate of DDTr degradation was much faster, with 40% decrease in DDTr concentration within 28h of NZVI addition. Here, the faster DDTr degradation may be through direct electron transfer between NZVI particles and DDTr molecules adsorbed on soil. Increase in the concentration of 4,4-DDD and 2,4-DDD during NZVI addition suggest that these compounds are either intermediate or end products of DDT degradation process.

Interaction of 2,4,6-trichlorophenol with high carbon iron filings: Reaction and sorption mechanisms

Reductive dehalogenation of 2,4,6-trichlorophenol (2,4,6-TCP) by two types of high carbon iron filings (HCIF), HCIF-1 and HCIF-2 was studied in batch reactors. While the iron, copper, manganese and carbon content of the two types of HCIF was similar, the specific surface area of HCIF-1 and HCIF-2 were 1.944 and 3.418m(2)g(-1), respectively. During interaction with HCIF-1, 2,4,6-TCP adsorbed on HCIF-1 surface resulting in rapid reduction of aqueous phase 2,4,6-TCP concentration. However, reductive dehalogenation of 2,4,6-TCP was negligible. During interaction between 2,4,6-TCP and HCIF-2, both 2,4,6-TCP adsorption on HCIF-2, and 2,4,6,-TCP dechlorination was observed. 2,4,6-TCP partitioning between solid and aqueous phase could be described by a Freundlich isotherm, while 2,4,6-TCP dechlorination could be described by an appropriate rate expression. A mathematical model was developed for describing the overall interaction of 2,4,6-TCP with HCIF-2, incorporating simultaneous adsorption/desorption and dechlorination reactions of 2,4,6-TCP with the HCIF surface. 2,4-Dichlorophenol (2,4-DCP), 2-chlorophenol (2-CP) and minor amounts of 4-chlorophenol (4-CP) evolved as 2,4,6-TCP dechlorination by-products. The evolved 2,4-DCP partitioned strongly to the HCIF surface. 4-CP and 2-CP accumulated in the aqueous phase. No transformation of 2-CP or 4-CP to phenol was observed.

Optimal choice of wastewater treatment train by multi-objective optimization

The typical domestic wastewater treatment train consists of some combination of unit operations for preliminary, primary, secondary, tertiary, and advanced treatment, and residual management, with many options being available for each type of unit operation. The challenge is to select treatment trains for which the extent and reliability of treatment are high, whereas the capital, operation and maintenance (O&M) costs of the treatment and land area requirement are low. This proposition has been formulated as a multi-objective optimization problem, and solved using the evolutionary/genetic optimization technique. The inputs required are the capital costs, O&M costs, land area requirements, and reliabilities of the unit operations of various types. In addition, overall environmental cost (E) corresponding to various treatment trains is input as a normalized parameter, which can take values in the range 0–100, with E being 100 corresponding to the ‘no treatment’ option. In other cases, E is a function of both treatment train efficiency and reliability. The problem was solved to determine the Pareto optimal, i.e. ‘no worse’ than each other, set of solutions under three conditions, viz. when E was not constrained, and for E<75, and E<50. Correctness of the algorithm was probed through a threefold analysis, (1) by solving a simplified two-objective problem, (2) by demonstrating the efficiency of the algorithm in picking up ‘sure-optimal’ solutions, i.e. solutions deliberately made optimal through manipulation of input data, and (3) by demonstrating that the set of optimal solutions remains approximately the same irrespective of the variations in the initial population size chosen for the genetic operations.

Development of socio-economic impact assessment methodology applicable to large water resource projects in India

SUMMARY The genesis of socio-economic impact assessment (SIA) in India is pressure from funding agencies like the World Bank, Asian Development Bank, and similar institutions. Of late, these institutions have stressed appraisal of environmental concerns as a pre-condition for financial support to large infra-structure projects. However, SIA studies are easier to conceptualise than to implement, because the issues involved are nebulous, complex, highly nuanced, difficult to define, and not easily amenable to quantification. These are some of the reasons for the cursory treatment of socioeconomic impact studies in India as a formality to satisfy monitoring and funding agency requirements and not as a tool for ensuring maximum social good through the developmental process. However, proper implementation of the concept of SIA in essential in attaining the goals of sustainable development. Ensuring social justice, i.e. preventing the continued impoverishment, displacement, social dislocation, and marginalisation of the weaker sections of Indian society, who always seem to bear the burden of adverse effects of such large infra-structure projects in disproportionate numbers, is also a goal of SIA. Increasing ambivalent attitudes and mounting opposition towards the implementation of large water resources projects of late in India necessitate systematic, transparent, and exhaustive consideration of all relevant socioeconomic issues before implementation of such projects. The objective of this study was to develop a comprehensive methodology for SIA for large water resource projects in India. The methodology was based on the review of the literature and other means and implicitly addresses the major goals of SIA — sustainable development and the achievement of social justice related to development.