Rajesh Roshan Dash

A review on chemical coagulation/flocculation technologies for removal of colour from textile wastewaters

Textile industry is one of the most chemically intensive industries on the earth and the major polluter of potable water. It generates huge quantities of complex chemical substances as a part of unused materials including dyes in the form of wastewater during various stages of textile processing. The direct discharge of this wastewater into environment affects its ecological status by causing various undesirable changes. As environmental protection becomes a global concern, industries are finding novel solutions for developing technologies that can diminish the environmental damage. However, colour removal from textile wastewater by means of cheaper and environmental friendly technologies is still a major challenge. In this manuscript, several options of decolourisation of textile wastewater by chemical means have been reviewed. Based on the present review, some novel pre-hydrolysed coagulants such as Polyaluminium chloride (PACl), Polyaluminium ferric chloride (PAFCl), Polyferrous sulphate (PFS) and Polyferric chloride (PFCl) have been found to be more effective and suggested for decolourisation of the textile wastewater. Moreover, use of natural coagulants for textile wastewater treatment has also been emphasised and encouraged as the viable alternative because of their eco-friendly nature.

Simultaneous removal of nitrogen and phosphorous from domestic wastewater using Bacillus cereus GS-5 strain exhibiting heterotrophic nitrification, aerobic denitrification and denitrifying phosphorous removal

A newly isolated GS-5 strain exhibiting heterotrophic nitrification, aerobic denitrification and denitrifying phosphorous removal was identified as Bacillus cereus GS-5 based on its phenotypic and phylogenetic characteristics. The isolate had exhibited efficient NH4+-N, NO3--N, NO2--N and PO43--P removal from nutrient spiked real domestic wastewater with average rates of 2.62, 2.69, 1.16 and 0.42mgL-1h-1, respectively under aerobic condition. Metabolic inhibitor based mass balance analysis indicated that dinitrogen gas (41%), intracellular nitrogen (29%) and intracellular phosphorous (60%) were the major fates of the initial NH4+-N and PO43--P. The successfully expression of hydroxylamine oxidase (hao), nitrate reductase (nar), nitrite reductase (nir) and poly phosphate kinase (ppk) enzyme in the cell free extracts and PCR amplification of nar, nir and ppk genes in the isolated strain provided further evidences for the nutrient removal possibility. A possible pathway of for nitrogen removal by GS-5 is suggested.

A mechanistic review on vermifiltration of wastewater: Design, operation and performance

With global population explosion, the available water resources are slowly being polluted due to the excessive human interference. To encounter this, it is the need of this hour to find out sustainable pollution remediating technologies to meet the stringent discharge standards for domestic as well as industrial wastewaters. In addition, those techniques should have the capabilities for effective implementation even in developing countries. Based on the available literatures, one such technique, named vermifilter, has been identified which takes care of almost all the sustainable and economical criteria for its effective implementation even in developing countries. The aim of this meta-analysis is to provide a comprehensive review on assessment mechanisms involved, factors affecting the process and performance of vermifiltration under different scenarios. The present review envisages the current state of the knowledge regarding physical, chemical and biological aspects related to the treatment mechanisms and effective functioning of earthworms. This review has also proposed several suggestive plans on its application at any proposed site.

Supremacy of Magnesium Chloride for Decolourisation of Textile Wastewater: A Comparative Study on the Use of Different Coagulants

In this study, treatment efficiency of magnesium chloride (MgCl2.6H2O) was compared with respect to ferrous sulphate (FeSO4.7H2O), polyaluminium chloride (PACl), and aluminium chlorohydrate (ACH) for the treatment of textile wastewater. Treatment efficiency was assessed in terms of decolourisation and chemical oxygen demand (COD) reduction of synthetic textile wastewater containing reactive, direct and disperse dyes, along with the other chemical constituents that are normally released from different textile processing units. MgCl2.6H2O/Lime produced colour removal efficiency of 99.68% at a dosage 1200mg/L for the wastewater containing all the three dyes together. MgCl2.6H2O/Lime was also found to be the most effective coagulant system for treatment of textile wastewater containing only reactive dye, which produced 99.73% colour removal at a dosage of 1100 mg/L. For both the direct and disperse dyes, ACH was found to be superior over MgCl2.6H2O/Lime, FeSO4.7H2O/Lime, and PACl. Industrial grade ACH, which is normally used as polyelectrolyte, for the first time was used as coagulant in this study and was also appeared to be significant for decolourisation of textile wastewater containing all the three dyes together. From this study, MgCl2.6H2O/Lime was recommended as the best coagulant for the decolourisation of textile wastewater having very high original pH.

Development of an integrated system for the treatment of rural domestic wastewater: emphasis on nutrient removal

With the aim of enhancing the nutrient removal from rural domestic wastewater while reducing the cost of the treatment process, a novel, integrated treatment system consisting of a multi-stage bio-filter with drop aeration and a post positioned attached growth carbonaceous denitrifying bio-reactor was designed and developed in this study. The bio-filter was packed with ‘dolochar’, a sponge iron industry waste, as an adsorbent mainly for phosphate removal through a physicochemical approach. The denitrifying bio-reactor was packed with many waste organic solid substances (WOSS) as carbon sources and substrates for biomass attachment, mainly to remove nitrate in the biological denitrification process. The performance of the modular system, treating real domestic wastewater was monitored for a period of about 60 days and the average removal efficiencies during the period were as follows: phosphate, 99.48%; nitrate, 92.44%, ammonia, 96.64%, with mean final effluent concentration of 0.153, 5.5, and 1.06 mg L−1, respectively. This treatment system would allow multipurpose reuse of the final effluent. Moreover, the saturated dolochar can be used as a nutrient supply in agricultural practices and the partially degraded carbonaceous substances can also be used as an organic fertilizer after composting. Thus, the system displays immense potential for treating domestic wastewater significantly by decreasing the concentrations of nutrient and most importantly, facilitating the conversion of the waste materials into usable ones.

Assessing Possible Applications of Waste Organic Solid Substances as Carbon Sources and Biofilm Substrates for Elimination of Nitrate Toxicity from Wastewater

AbstractThis work aimed to find inexpensive alternatives that could serve both as carbon source and biofilm carrier for heterotrophic denitrification in treating nitrate contaminated waters. To asc...

Understanding intricacies of clogging and its alleviation by introducing earthworms in soil biofilters

With the scarcity of fresh water and rise in pollution load in the aquatic ecosystem over the globe, the domestic and industrial effluents need to be reused after suitable treatment. In an attempt to do so, soil biofilters have been identified as a treatment alternative that is suitable for application in developing countries. However, rapid development of clogging in the soil biofilters limits its applicability as an effective technology. This paper aims to understand the occurrence of clogging due to biofilms formation in and over the bedding of soil media. To address this, the organic loading rates (OLRs) were varied in the range of 2.25-11.25kgCOD/m3·day to create different degree of clogging. Earthworms were inoculated into the soil bedding at the earthworm densities (EWDs) of 0, 5000 and 10,000earthworms/m3 to study the effect of earthworms introduction on clogging. The degree of clogging was measured using clogging coefficient (CC), hydraulic conductivity and head loss. The study highlights the impact of earthworms on the removal performance and clogging of soil biofilter. For all earthworm densities, head loss and clogging coefficient increased and hydraulic conductivity decreased linearly with organic loading rate. Introduction of earthworms versus no earthworms resulted in lower head loss and clogging coefficient and higher hydraulic conductivity for all organic loading rates, while increasing EWD from 5000 to 10,000 had only marginal effects on all parameters. The study reveals that high organic loading rate activates higher number of microbial sites, in turn causing higher degree of clogging. However, the introduction of earthworms reduces the clogging rate significantly along with enhanced treatment performance. The outcome of this study indicates that incorporation of earthworms into the soil biofilter can reduce the degree of bio-clogging and might provide a highly sustainable, low cost and efficient treatment system for the developing countries.

COD removal index — A mechanistic tool for predicting organics removal performance of vermifilters

The present study was aimed at developing a mathematical COD removal index (CRI) based on the key variables of vermifiltration such as hydraulic retention time (HRT), organic concentration and earthworm density (EWD). In the maiden attempt of framing such an index, many experimental runs were conducted by varying the COD strength of the wastewater from 2.0-4.0 kg/m3, EWD and HLR were from 0 to 10,000 earthworms/m3 and 1.8-4.5 m3/m2·d, respectively. The sensitivity analysis of the developed CRI reveals that the EWD, bedding volume, concentration of organics and the flow applied to the vermifilter can immensely affect the model response. However, flow applied to the system is observed to be the most sensitive among other parameters incorporated in the model. In addition, from the sensitivity analysis, it was also revealed that the removal efficiencies were observed to increase with the increase in CRI values in the COD range of 0.2-6.0 kg/m3. In addition, the plot between the reported removals from literatures on vermifiltration of domestic wastewater and CRI values yielded an R2 value of 0.76. Such a high correlation suggests that the developed CRI index can be applied for other wastewaters also. The results of this study indicate that the developed index can successfully be applied in determining and predicting organics removal from vermifiltration of wastewaters.

Optimization of organics removal and understanding the impact of HRT on vermifiltration of brewery wastewater

The study was conducted with an aim to optimize the parameters involved in removing organics from brewery effluents using a newly developed horizontal subsurface flow vermifilter. It was also aimed at understanding the impact of hydraulic retention time (HRT) on the vermifiltration of brewery wastewater. With the help of Box-Behnken design (BBD) and response surface methodology, optimization of the COD removal from the vermifiltration was carried out. The parameters chosen for the optimization were hydraulic loading rate (HLR), organics strength and earthworm densities (EWDs). The model obtained from the response surface methodology (RSM) analysis was a quadratic polynomial model with R2 value of 0.99. The optimal conditions for achieving maximum chemical oxygen demand (COD) removal were at influent COD concentration of 3542.22 mg/L, EWD of 9661.33 earthworms/m3 and HLR of 1.84 m3/m2·d. At the optimum conditions, COD removal of 94.99% was obtained against the predicted value of 95.85%. Verification of the model on real brewery wastewater also showed minimal error against the predicted COD removal. The COD, total nitrogen (TN) and total phosphorous (TP) removal at the HRT of 10.66 h were found to be 73.88%, 18.13% and 39.04%, respectively. Whereas, The COD, TN and TP removals at the HRT of 26.66 h were 96.24, 21.57 and 43.3%, respectively.

Effectiveness Study of Dolochar as a Filter Media in Wastewater Filtration

The study was carried out to evaluate the feasibility of slow sand filter by using dolochar, a solid waste generated from sponge iron industry, as a filter media and compared with the sand media filter. Effectiveness of slow sand filters assessed by two laboratory-scale filter columns (10 cm diameter and 0.40 m media depth): one consisting sand media and other with dolochar. The effective size of both sand and dolochar media used were 0.42 mm to study the performance at filtration rate of 0.06 m/h. For 160 h of run period, the dolochar media showed higher removal efficiencies, especially chemical oxygen demand (COD) removal up to 89% compared to sand media filter of 69%, turbidity removal of 96% compared to 90% of sand media filter, and phosphate removal also observed more in case of dolochar media filter—especially, the phosphate removal from the dolochar media filter was up to 92.71% compared to sand filter of 85.24%. Since the dolochar media filter exhibited to possess higher removal efficiencies, it supports the utility of dolochar as a low cost and highly efficient filter media for slow sand filtration.