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In the present study, sludge produced from the continuous defluoridation set-up was used as partial replacement for fine aggregates in mortar making. Aluminium sulphate (alum) and polyaluminium chloride (PACl) were used as coagulants for fluoride removal and mortar cubes with size of 50 mm × 50 mm × 50 mm were prepared with alum and PACl sludge in different proportions, i.e. 0%, 1%, 2%, 3%, 4% and 5%. The compressive strength tests were conducted and it was observed that the strength of mortar with 1% replacement increased by 2.5% for alum sludge and 6% for PACl sludge and the compressive strength showed satisfactory values up to 3% sludge replacement for alum and PACl sludge. The impact of partially replacing alum and PACl sludge on the strength of mortars regarding calcium silicate hydrate gel, silica and other hydration products was studied. Toxic Characteristics Leaching Procedure was performed for the mortars and aluminium concentration was within the permissible limits of 0.2 ppm. The results suggested that the reuse of alum and PACl sludges can lead to new paths in reducing the deterioration of the ecosystem because of waste disposal.

Measurement of nitrate nitrogen is relatively less easy and reliable, given the complexity of analytical procedures already marred by interferences. Interfering constituents like organics a...

This paper explores the effect of hybrid chlorine and UV disinfection treatment against their individual usage on microbial community, functional genes, antibiotic resistant genes (ARGs) and disinfection by-products (DBPs) formation. The disinfectant doses of 2.5 mg L−1 chlorine and 41 mJ cm−2 UV were selected based on the coliform counts to be attained in treated sewage. The highest bacterial diversity was observed in control (secondary treated) sample followed by UV, chlorine and hybrid disinfection. The highest elimination of bacterial species (296) was achieved in hybrid treatment, which was far better than the standalone treatments. The disinfection with all the disinfectants used resulted in increased abundance of ARGs. Motility genes were found to be enriched in hybrid disinfected samples. DBP concentrations were within the stipulated norms for all the disinfectant treatments used. Hybrid disinfection was observed to be more effective in alleviating the risks associated with the reuse of treated sewage.

Continuous upflow pilot plants based on conventional clariflocculation (CC) and pulsating floc blanket clarification (PFBC) technologies were designed and fabricated for a capacity to treat about 8,000 L/day, to understand the fundamental differences in their functioning and assess their relative performance, especially under low turbidity conditions. Influent turbidity varying from 2 to 10 NTU was treated using coagulant alum, and efficiency of CC and PFBC in terms of average turbidity removal was found to be 23% and 48%, respectively. On observing this vast difference, it was postulated that total residual aluminum should also be lower in water treated from PFBC. Experiments and MLR analysis confirmed the hypothesis, with residual aluminum ranging from 0.055 to 0.040 mg/L and 0.036 mg/L to below detectable levels for CC and PFBC, respectively. These findings are of high significance, since minimization of residual aluminum in drinking water is a priority of WHO due to its reported neurotoxicity and can be complied with simple replacement of CC with PFBC. PRACTITIONER POINTS: Pulsating floc blanket clarifier (PFBC) performed better than conventional clariflocculator (CC) in terms of turbidity removal. Pulsating floc blanket allowed more effective utilization of coagulant alum, resulting in significantly lower residual aluminum in clarified water. Turbidity levels of influent and effluent are related to residual aluminum in treated water. PFBCs are more compact and modular, and can facilitate a good alternative to CCs.

The requirement of large land area limits the adoption of constructed wetlands (CWs) in urban settings with limited land availability. The area calculations for CW design are commonly carried out following Kikuth approach where the removal rate constant (K) is derived from literature. Investigation of secondary data of 82 vertical flow CWs, performed in this study, yielded wide variations (0.0003 - 0.822 md

Chlorination has been employed extensively for sewage disinfection so that it can be reused, but the health issues related to its disinfection byproducts (DBPs) have forced to search for safer options. The present study focuses on the efficiency of chlorine disinfection on five dominant coliform bacterial species present in the secondary treated effluent. Resistance to low doses of chlorine was observed by few coliform species, such as Serratia/Hafnia which in turn required much higher doses of chlorine to achieve Total Coliform Count (TCC) within standards. This consequently increased formation of DBPs. A quadratic model of design of experiments (DOE) softaware was opted as an optimization strategy for chlorination, which was attempted to achieve counts for rest of the species to be brought within standard except for resistant ones so that the initial disinfection with chlorine could be terminated at this dose. This would then be followed by another disinfectant (UV/Ozone) against which such resistance among those species was not observed. The optimized results of chlorination (2.5 ppm of CD at 14.83 min/42 mg-min/L) would be useful in designing a hybrid disifection strategy which may help reduce the CD substantially and thereby its byproducts. Analysis of four Trihalomethanes (THMs) was carried out with the help of Gas chromatography-mass spectrometry and gas chromatography/tandem mass spectrometry (GC–MS/MS) to assess their concentrations due to chlorination of sewage. The effect of chlorine on physiology of bacterial cells was also examined through scanned electron microscopy (SEM) analysis to get a clue to inactivation mechanism.

Management of bacterial survival post chlorine disinfection is vital for safe wastewater reuse for irrigation, as the presence of microorganisms in large numbers may lead to subsequent contamination of the surface and ground water reservoirs. Even after satisfying the current norms of coliform counts after disinfection (less than 1000 MPN per 100 mL), chlorine tolerant bacteria surviving in inadequately treated wastewater may pose a public health threat as many of these bacteria are able to re-grow upon storage. The current study is aimed to assess the magnitude of the problem posed by chlorine tolerant bacteria during chlorine disinfection and attempts to derive a strategy for safe disinfection. The chlorine tolerance was examined in the dominant gram negative bacteria (GNB) recovered from secondary treated sewage from a treatment plant located at Jaipur, India. Bacterial survival and re-growth (after 24 h) studies on test species (n = 11) with reference to E.coli ATCC 25922 reveal that, while the lethal doses of isolates ranged from 0.5 to 1.25 mgL−1,the chlorine doses for complete inhibition of re-growth were much higher (0.75–1.75 mgL−1).The isolates showing highest lethal dose and re-growth inhibition dose, identified as Citrobacter freundii, Klebsiella sp. and Stenotrophomonas maltophilia also exhibited very low log effective reduction (0.72–1.90) values and were selected as chlorine tolerant bacteria. Results of inactivation kinetics experiments on chlorine tolerant bacteria reveal a strong correlation (R2 > 0.89–0.99) between log reduction values and contact time. In re-growth kinetics experiments, maximum re-growth was observed after 6 h exposure following which, only marginal increase was registered up to 24 h. The study indicates that the existing approach of bacterial elimination post chlorine treatment may be grossly inadequate to assess the performance of the disinfection process adopted for drinking water treatment. It further brings out a novel approach to arrive at meaningful chlorine doses that take bacterial re-growth into account for achieving safe disinfection.

Globally estrogenic pollutants are a cause of concern in wastewaters and water bodies because of their high endocrine disrupting activity leading to extremely negative impacts on humans and other organisms even at very low environmental concentrations. Bioremediation of estrogens has been studied extensively and one technology that has emerged with its promising capabilities is Bioelectrochemical Systems (BESs). Several studies in the past have investigated BESs applications for treatment of wastewaters containing toxic recalcitrant pollutants with a primary focus on improvement of performance of these systems for their deployment in real field applications. But the information is scattered and further the improvements are difficult to achieve for standalone BESs. This review critically examines the various existing treatment technologies for the effective estrogen degradation. The major focus of this paper is on the technological advancements for scaling up of these BESs for the real field applications along with their integration with the existing and conventional wastewater treatment systems. A detailed discussion on few selected microbial species having the unusual properties of heterotrophic nitrification and extraordinary stress response ability to toxic compounds and their degradation has been highlighted. Based on the in-depth study and analysis of BESs, microbes and possible benefits of various treatment methods for estrogen removal, we have proposed a sustainable Hybrid BES-centered treatment system for this purpose as a choice for wastewater treatment. We have also identified three pipeline tasks that reflect the vital parts of the life cycle of drugs and integrated treatment unit, as a way forward to foster bioeconomy along with an approach for sustainable wastewater treatment.

Chlorine tolerance is a major concern during disinfection of treated wastewater. Here, the UV disinfection efficacy was assessed for controlling two previously reported chlorine tolerant bacteria, Stenotrophomonas maltophilia and Klebsiella sp. along with a standard E.coli strain using a collimated beam apparatus. UV exposure was applied in two sets - short exposure (0–60 s) and long exposure (0–60 min). Bacterial counts immediately after, and 24 h post irradiation (regrowth) were analysed using media plating. Morphological characteristics and intracellular Mn/Fe ratio were examined by SEM and ICP-OES respectively, to understand the possible reasons for sensitivity/ resistance to irradiation. E.coli and Klebsiella sp. were effectively reduced (> 4 log) but S. maltophilia showed low Effective Reduction (ER

Ozone is an attractive disinfection alternative to chlorine as chlorine has some environmental consequences due to its disinfection byproducts potential. In the present study ozone was used for the disinfection of secondary treated effluent of sewage treatment plant which is based on rotating biological contactor, process, Malaviya National Institute of Technology (Jaipur). From the experimental results it was found that ozone dose of 30 mg/L was required to achieve WHO standards for Total Coliform Count (TCC) of 1000 CFU/100 mL for food crop irrigation and recreational impoundments. One factorial design method of response surface methodology (RSM) was used for statistically obtaining optimum ozone dose that satisfies the norms for COD and TCC simultaneously. The optimized ozone dose suggested by the model was 30 mg/L to bring TCC within norms and the value of COD at this dose was 21 mg/L. Experimental verification of the results was in good agreement with the predicted results of one factorial design. Analysis of scanned electron microscopy (SEM) images, shows the effect of ozone doses on bacterial cell membrane. Effect of ozone on four trihalomethanes was also studied using GC–MS/MS.

Acyclovir (ACV) prescribed for treating a wide range of viral infections has found its way into the aquatic environment. It is emerging as a major concern for water bodies and biota due to its ecotoxicological effects. The objective of this study is to provide a comprehensive critical review of available chemical, biological, and hybrid techniques of ACV removal from water, compare their relative efficacies under different environmental conditions, and to draw attention towards emerging areas of research necessitating future studies. Though the present review is dedicated to ACV removal, however, the removal strategies are similar and can be extrapolated for the removal of other micro-pollutants. This work also provides an overview of the literature on the occurrence of ACV in industrial effluents, WWTPs, surface waters, groundwater, and reservoirs. At the end, the paper explores inadequately researched gray areas that require further studies on mathematical modeling and simulation, thermodynamics, reaction pathways during degradative removal, toxicological studies on transformation products (TPs), and on complete mineralization as TPs have been reported to be more toxic than ACV itself.

An extensive chemical analysis was conducted on water samples and fouled membranes of community Reverse Osmosis plants of Rajasthan, India facing accelerated scaling. Calcium carbonate was the major foulant as evidenced by the rhombohedral crystalline structure with sharp edges in SEM images of membranes of one of the plants while the other membrane had deposits of aragonite having outward-oriented needles. The reverse solubility of CaCO3 with temperature was the major reason behind carbonate scaling as the area witnesses ambient temperatures of more than 40 °C for many months of the year. To further explain the scaling process, a detailed chemical analysis of five recently established plants was carried out and verified by ion balance. It was found that consecutive combination of Ca2+ and Mg2+ with F−, CO32- and SO42- would give the best quantification of scale formation. Extent of CaCO3 scaling was also verified through Langelier Saturation Index and Ryznar Stability Index. The earlier part of this study resulted in promotion of the use of antiscalants in these plants, leading to sharp increase in the membrane life. Therefore, reject and raw samples were analyzed in presence and absence of antiscalant in the feed supply. The molar ratios of ions clearly revealed the inefficiency of antiscalant in arresting the growth of sulfate scales. As a result, many other inorganic deposits besides carbonates require further research inputs.

The removal of fluoride from drinking water by the method of adsorption on activated alumina is found superior than other defluoridation techniques mostly due to the strong affinity between aluminium and fluoride. Dissolution of aluminium from the alumina surfaces into its free and hydroxide ions in the aqueous medium is reported to be very low, but the presence of high fluoride concentrations may increase its solubility due to the formation of monomeric aluminium fluoride and aluminium hydroxyl fluoride complexes. An Activated Alumina Defluoridation Model Simulator (AAD) has been developed to represent fluoride adsorption on the basis of the surface complexation theory incorporating aspects of aluminium solubility in presence of high fluoride concentrations and pH variations. Model validations were carried out for residual aluminium concentrations in alumina treated water, by conducting a series of batch fluoride adsorption experiments using activated alumina (grade FB101) treating fluoride concentrations of 1-10mg/L, at varying pH conditions. The total residual aluminium in the defluoridated water is due to presence of both dissolved and precipitated Al-F complexed forms. The Freundlich adsorption isotherm was found fit for fluoride adsorption capacity versus residual fluoride concentrations for pH=7.5, and the relationship is given by the linearised equation log(x/m)=logk+(1/n) logC(e) with values of k=0.15mg/g and 1/n=0.45 indicating favorable adsorption. The relationship is linear in the region of low fluoride concentrations, but as concentrations of fluoride increased, the formation of the dissolved AlF(3)(0) complexes was favored than adsorption on alumina, and hence makes the isotherm nonlinear. The AAD simulations can predict for operating fluoride uptake capacity in order to keep the residual aluminium within permissible limits in the alumina treated water.

Nitrate nitrogen levels upto 425 mg l−1 (D.O = 2.5 mg l−1) were treated under aerobic conditions by activated sludge mixed with Thiosphaera pantotropha. Efficiency of nitrate nitrogen removal ranged from 75–85% for different reactors operated at HRT between 0.5 to 1 day and SRT of 2–8 days.

Simultaneous nitrification\aerobic denitrification studies of a high strength synthetic nitrogenous fertilizer wastewater in a single stage were carried out using a rotating biological contactor (RBC). Mixed culture biofilm consisting of Nitrifiers and Thiosphaera pantotropha (a heterotrophic nitrifier and aerobic denitrifier) was acclimated to 1386 mg l‐1 of TKN & 400 mg l‐1 of nitrate nitrogen. The effect of different nitrogen loadings and hydraulic retention times (HRTs) on percentage removal of TKN and nitrate nitrogen simultaneously, was investigated. A maximum TKN removal of 95.6 percent could be achieved at a nitrogen loading of 9.36 gN m‐2 d‐1 and HRT of 2 days. The results showed that the process is zero order with respect to nitrogen removal. The HRT studied were in the range of 0.5–3 days. The corresponding percentage TKN removal ranged from 43.9–93.7. Nitrate removal of 97–98% could also be achieved simultaneously. Nitrite accumulated significantly throughout these studies. Nitrogen l...

High strength domestic wastewater discharges after no/partial treatment through sewage treatment plants or septic tank seepage held systems have resulted in a large build-up of groundwater nitrates in Rajasthan, India. The groundwater table is very deep and nitrate concentrations of 500-750 mg/l (113-169) as NO3--N) are commonly found. A novel biofilm ill a 3-stage lab-scale rotating biological contactor (RBC) was developed by the incorporation of a sulphur oxidising bacterium Thiosphaera pantotropha which exhibited high simultaneous removal of carbon and nitrogen in Fully aerobic conditions. T. pantotropha has been shown to be capable of simultaneous heterotrophic nitrification and aerobic denitrification thereby helping the steps of carbon oxidation, nitrification and denitrification to be carried out concurrently. The first stage having T. pantotropha dominated biofilm showed high carbon and NH4+-N removal rates of 8.7-25.9 g COD/m(2) d and 0.81-1.85 g N/m(2) d for the corresponding loadings of 10.0-32.0 g COD/m(2) d and 1.0-3.35 g N/m(2) d. The ratio of carbon removed to nitrogen removed was close to 12.0. The nitrification rate increased from 0.81 to 1.8 g N/m(2) d with the increasing nitrogen loading rates despite a high simultaneous organic loading rate. However, it fell to 1.53 g N/m(2) d at a high load of 3.35 g N/m(2) d and 32 g COD/m(2) d showing a possible inhibition of the process. A simultaneous 44-63% removal of nitrogen was also achieved without any significant NO2--N or NO3--N build-up. The second and third stages. almost devoid of any organic carbon, acted only as autotrophic nitrification units, converting the NH4+ -N from stage 1 to nitrite and nitrate. Such a system would not need a separate carbon oxidation step to increase nitrification rates and no external carbon source for denitrification, The alkalinity compensation during denitrification for that destroyed in nitrification may also result in a high economy. (C) 2001 . .

A mixed culture biofilm was developed with a sulfur oxidising, heterotrophic bacterium Thiosphaera pantotropha , autotrophic nitrifiers and other heterotrophs in a three stage rotating biological contactor (RBC). Specific benefits due to peculiar properties of T. pantotropha of simultaneous heterotrophic nitrification and aerobic denitrification were derived in the reactor investigated for a combined carbon and nitrogen removal from a synthetic domestic sewage. The first stage biofilm which contained T. pantotropha showed high COD and NH 4 + -N removal rates of 5.8–14.1 g COD/m 3 ·d and 0.47–1.1 g N/m 2 ·d for the corresponding loading rates of 6.9–20.7 g COD/m 3 ·d and 0.69–2.09 g N/m 2 ·d, respectively. Contrary to the conventional units designed for a concurrent carbon removal and nitrification, the nitrification rates increased linearly with an increase in organic loading rate before stabilising at about 1 g N/m 2 ·d corresponding to a COD loading rate of about 15 g/m 2 ·d and a nitrogen loading rate of 1.5 g N/m 2 ·d showing a change in the order of reaction from first to zero. A simultaneous nitrogen removal of 20–68% was also obtained. The system's performance indicated that a single stage aerobic biofilm can be developed to meet the increasingly stringent regulations on effluent nitrogen discharges affording several advantages over the conventional systems, e.g. low buffer requirements, no need for external carbon source for denitrification, etc., which may result in substantial reduction in the treatment cost.