Anil K. Saroha

Electrocoagulation for the treatment of textile industry effluent – A review

Various techniques such as physical, chemical, biological, advanced oxidation and electrochemical are used for the treatment of industrial effluent. The commonly used conventional biological treatment processes are time consuming, need large operational area and are not effective for effluent containing toxic elements. Advanced oxidation techniques result in high treatment cost and are generally used to obtain high purity grade water. The chemical coagulation technique is slow and generates large amount of sludge. Electrocoagulation has recently attracted attention as a potential technique for treating industrial effluent due to its versatility and environmental compatibility. This technique uses direct current source between metal electrodes immersed in the effluent, which causes the dissolution of electrode plates into the effluent. The metal ions, at an appropriate pH, can form wide range of coagulated species and metal hydroxides that destabilize and aggregate particles or precipitate and adsorb the dissolved contaminants. Therefore, the objective of the present manuscript is to review the potential of electrocoagulation for the treatment of industrial effluents, mainly removal of dyes from textile effluent.

Risk analysis of pyrolyzed biochar made from paper mill effluent treatment plant sludge for bioavailability and eco-toxicity of heavy metals

The risk analysis was performed to study the bioavailability and eco-toxicity of heavy metals in biochar obtained from pyrolysis of sludge of pulp and paper mill effluent treatment plant. The sludge was pyrolyzed at different temperatures (200-700°C) and the resultant biochar were analyzed for fractionation of heavy metals by sequential extraction procedure. It was observed that all the heavy metals get enriched in biochar matrix after pyrolysis, but the bioavailability and eco-toxicity of the heavy metals in biochar were significantly reduced as the mobile and bioavailable heavy metal fractions were transformed into the relatively stable fractions. Moreover, it was observed that the leaching potential of heavy metals decreased after pyrolysis and the best results were obtained for biochar pyrolyzed at 700°C.

Synthesis of the magnetic biochar composites for use as an adsorbent for the removal of pentachlorophenol from the effluent.

The zero-valent iron magnetic biochar composites (ZVI-MBC) were synthesized from the paper mill sludge biochar and used for the treatment of the synthetic and real effluent containing pentachlorophenol (PCP). During the synthesis of ZVI-MBC, NaBH4 was used as the reducing agent to reduce Fe(II) to Fe(0) and cetyltrimethylammonium bromide was added as surfactant. The effect of the molar ratio of FeSO4 to NaBH4, dose of the surfactant and the ZVI to biochar ratio on the PCP removal efficiency was investigated. It was found that the ZVI-MBC combines the advantages of biochar and ZVI particles for the simultaneous adsorption and dechlorination of PCP in the effluent and the complete removal of PCP was obtained. The ageing tests showed that biochar prevents the formation of oxide film on the ZVI particles and leaching tests confirmed the stability of ZVI on biochar matrix as very low iron leaching was noticed.

Utilization of sludge based adsorbents for the removal of various pollutants: A review

Sludge based adsorbents are widely used for the removal of various pollutants from water and wastewater systems and the available data is much diversified. The purpose of this review is to organize and critically review the scattered available information on the potential of use of sludge based adsorbents for the removal of various pollutants. It was observed that performance of the sludge based adsorbents varies depending on the type of pollutants, type of precursor sludge, carbonization time-temperature profile and the type of activation conditions used. The variation in pyrolysis and activation conditions found to directly affect the adsorbent properties, adsorption capacity and the mechanism of pollutant removal by sludge based adsorbents. The interaction mechanisms of pollutants with adsorbent surface found to have a detrimental effect on desorption and regeneration of the adsorbents and its recycling potential. Therefore, desorption and regeneration technique used for recycle of the adsorbents is also discussed in detail. Moreover, life cycle and cost analysis of sludge based adsorbents is assessed to ensure the cost effectiveness of their application in water treatment operations.

Effect of pyrolysis temperature on polycyclic aromatic hydrocarbons toxicity and sorption behaviour of biochars prepared by pyrolysis of paper mill effluent treatment plant sludge

The polycyclic aromatic hydrocarbons (PAHs) toxicity and sorption behaviour of biochars prepared from pyrolysis of paper mill effluent treatment plant (ETP) sludge in temperature range 200-700 °C was studied. The sorption behaviour was found to depend on the degree of carbonization where the fractions of carbonized and uncarbonized organic content in the biochar act as an adsorption media and partition media, respectively. The sorption and partition fractions were quantified by isotherm separation method and isotherm parameters were correlated with biochar properties (aromaticity, polarity, surface area, pore volume and ash content). The risk assessment for the 16 priority EPA PAHs present in the biochar matrix was performed and it was found that the concentrations of the PAHs in the biochar were within the permissible limits prescribed by US EPA (except BC400 and BC500 for high molecular weight PAHs).

Electrochemical Treatment of Distillery Spent Wash Using Aluminum and Iron Electrodes

Abstract Electrochemical treatment of distillery spent wash was carried out using different combinations of aluminum and iron electrodes in batch mode of operation. The spent wash was characterized for various parameters as per standard method of analysis and the treatment results were analyzed in terms of chemical oxygen demand (COD) removal efficiency of the spent wash. The experiments were performed to study the effect of operating parameters such as current density, pH of the spent wash, agitation speed, electrolysis time and the distance between the electrodes on the COD removal efficiency of the spent wash. It was observed that aluminum electrodes were more suitable for treatment of distillery spent wash as compared to iron electrodes. The maximum COD removal efficiency of 81.3% was obtained with Al-Al electrodes at the current density of 0.187 A·cm −2 and pH 3 for an electrolysis time of 2 h.

Electrochemical Treatment of Effluent from Small-Scale Dyeing Unit

Abstract Electrochemical treatment of small-scale dyeing unit effluent containing Reactive Yellow 86, Indanthrene Blue RS, Basic GR 4 and Reactive Yellow 145 dyes was carried out with aluminium electrodes in batch mode of operation. The effluent was characterized for various parameters. The experiments were performed for 120 min, keeping the inter-electrode distance at 3 cm with a current density of 0.0625 A/cm2; the colour removal efficiency was determined for each of the four dyes. A colour removal efficiency of >97% was obtained for each of the dyes for an electrolysis time of 120 min. Further experiments were performed using aluminium sulphate as chemical coagulant to compare the colour removal efficiencies obtained by electrocoagulation and chemical coagulation.

Improvement in performance of sludge-based adsorbents by controlling key parameters by activation/modification: A critical review

ABSTRACT The conversion of sludge into an adsorbent is emerging out as a sustainable alternative for management of the sludge that otherwise considered as a waste. The poor performance of the sludge-based adsorbents limits their practical applications. Different methods and techniques have been reported in literature to improve the performance of sludge-based adsorbents. The data are so diversified that it is become difficult to choose the potential modification/activation techniques to get desired adsorbent performance. In this review we made efforts to correlate the modification/activation technique parameters with performance-controlling parameters (surface area, porosity, surface functionalities, ash content, carbon content). A detailed description of effect preparation and activation techniques on adsorbent properties have been provided. Various physical and chemical activation techniques are discussed in detail. Furthermore, the variation in processing and modification/activation conditions contributes to the differences in the cost involved in the adsorbent preparation. Efforts have been made to materialize the gross cost estimate of the adsorbent to increase their practical applications.

Optimization of Pyrolysis Conditions to Synthesize Adsorbent from Paper Mill Sludge

Pyrolysis temperature is the key factor influencing the biochar yield. Experiments were performed to study the effect of pyrolysis temperature and additive dose on biochar yield. It was observed that biochar yield decreased with an increase in pyrolysis temperature and maximum yield was obtained at 300 o C. Conversely, surface area of the biochar increased with an increase in temperature and maximum surface area was obtained at 700 o C. The biochar was impregnated with different dosage of CaCO 3 to analyze the effect of CaCO 3 as an additive dosage on biochar properties. Addition of CaCO 3 significantly affects the surface area and pore volume of the biochar, although it does not lead to significant change in biochar yield. Batch experiments were performed to explore the potential of raw and impregnated biochar as an adsorbent for the removal of pentachlorophenol (PCP). A removal efficiency of 86% and 97% was obtained with raw biochar and 3% CaCO 3 impregnated biochar respectively.

Performance of various catalysts on treatment of refractory pollutants in industrial wastewater by catalytic wet air oxidation: A review

The tremendous increase of industrialization and urbanization worldwide causes the depletion of natural resources such as water and air which urges the necessity to follow the environmental sustainability across the globe. This requires eco-friendly and economical technologies for depollution of wastewater and gases or zero emission approach. Therefore, in this context the treatment and reuse of wastewater is an environmental friendly approach due to shortage of fresh water. Catalytic wet air oxidation (CWAO) is a promising technology for the treatment of toxic and non-biodegradable organic pollutants in the wastewater generated from various industries. Various heterogeneous catalysts have been extensively used for treatment of various model pollutants such as phenols, carboxylic acids, nitrogenous compounds and different types of industrial effluents. The present review focuses on the literature published on the performances of various noble and non-noble metal catalysts for the treatment of various pollutants by CWAO. Reports on biodegradability enhancement of industrial wastewater containing toxic contaminants by CWAO are reviewed. Detailed discussion is made on catalyst deactivation and their mitigation study and also on the various factors which affects the CWAO reaction.