Treatment of tannery wastewater by electrocoagulation

Treatment of tannery wastewater by electrocoagulation with low cell current （≤ 1A） and soluble electrodes （mild steel electrodes and aluminum electrodes） was studied. Compared with aluminum electrodes, mild steel electrodes were more effective for the removal of sulfide, with a removal efficiency of over 90%. But during the treatment process, black color precipitate typical to iron（Ⅱ） sulfides was produced. While aluminum electrodes were effective to eliminate the colority of the effluent, the removal efficiency of sulfide was lower than 12%. The mechanisms of the removal of chemical oxygen demand, ammonia, total organic carbon, sulfide and colority with the two soluble electrodes （mild steel and aluminum electrodes） were discussed in detail. In order to exert the predominance of diffenent types of electrodes, the tannery wastewater was treated using mild steel electrodes first followed by the filter and finally by the aluminum electrodes, the elimination rates of chemical oxygen demand, ammonia, total organic carbon, sulfide and colority were 68.0%, 43.1%, 55.1%, 96.7% and 84.3%, respectively, with the initial concentrations 2413.1 mg/L, 223.4 mg/L, 1000.4 mg/L, 112.3 mg/L and 256 dilution times, respectively. The absorbance spectra and energy consumption during electrocoagulation process were also discussed.

Removing contaminants from tannery wastewater by chemical precipitation using CaO and Ca(OH)2

The removal of Cr,sulfates and Chemical Oxygen Demand(COD)from industrial tannery wastewater by chemical precipitation was carried out using Calcium oxide(CaO)and Calcium hydroxide(Ca(OH)2).Different doses of alkalis,ranging from deficiency to excess hydroxyl species over the stoichiometric necessary,were used to remove theoretically the 100%of Cr[0.3-3.2 g alkali·(g Cr^3+)^-1].The precipitation was carried out at room temperature,10 min of vigorous stirring,200 r·min^-1 and a settling time of 24 h,followed by separation and characterization of liquid product.As result of addition of alkalis,pH underwent increase as did the alkali concentration.The removal of Cr,and sulfates also increased as alkali concentration did,although for first species the changes at higher alkali contents were less evident.COD removal on the other hand,did not follow a unique trend,instead exhibited a maximum.Based on our results,selection of a specific dose of alkali was carried out taking as reference the efficiency on total chromium removal,keeping the pH in the range 7 to 9 to ensure Cr precipitation as chromium hydroxide.With those conditions,jar test was used to produce enough liquid product in order to determine the removal percent of several other species.The removal percent of the species was as follows:Cr,SO4^2-,ZnSO4,FeSO4,CN^-1,NiSO4,Fe2[Fe(CN)6]at 99.8%,66.9%,99.6%,21.4%,70.9%,52.8%and 76.4%with CaO,and 99.8%,61.6%,99.9%,7.1%,84.0%,54.4%and 90.5%with Ca(OH)2,respectively.

Tannery wastewater treatment:conventional and promising processes,an updated 20-year review

Mismanagement of various wastes especially waste water produced by tanning processes has caused serious environmental problems and ultimately impaired human health.Constant efforts have been making to alleviate the pollution of tannery wastewater(TWW),yet terminal treatment still takes dominance.In this review,research onTWW treatment from 2000 to 2021 was summarized,and main methods such as coagulation and flocculation,adsorption,biological treatment,membrane filtration,advanced oxidation process were briefly discussed.More detailed introduction was given to the method of electrochemical treatment since it has excellent performance such as environmental friendliness and high efficiency,hence attracting more and more research attention in recent years.In view of the harsh physi-chemical conditions of TWW,integrated or combined treatment methods are accordingly recommended with better performance and multi-function,however comprehensive studies on optimization of methods combination and cost-effectiveness are needed.The certain issues that the residue Cr in treatment sludge and high salinity in effluent still remain were put forward in this work and potential solutions were provided.Moreover,this review proposed the perspective that realizing multi-function,recycling,and intensification should be the developing direction for future TWW treatment.This review is expected to provide a general guide for researchers who aspire to ameliorate TWW pollution problems and understand various methods utilized in this field.

Tannery wastewater treatment:conventional and promising processes,an updated 20-year review

Mismanagement of various wastes especially waste water produced by tanning processes has caused serious environmental problems and ultimately impaired human health.Constant efforts have been making to alleviate the pollution of tannery wastewater(TWW),yet terminal treatment still takes dominance.In this review,research on TWW treatment from 2000 to 2021 was summarized,and main methods such as coagulation and flocculation,adsorption,biological treatment,membrane filtration,advanced oxidation process were briefly discussed.More detailed introduc-tion was given to the method of electrochemical treatment since it has excellent performance such as environmental friendliness and high efficiency,hence attracting more and more research attention in recent years.In view of the harsh physi-chemical conditions of TWW,integrated or combined treatment methods are accordingly recommended with better performance and multi-function,however comprehensive studies on optimization of methods combina-tion and cost-effectiveness are needed.The certain issues that the residue Cr in treatment sludge and high salinity in effluent still remain were put forward in this work and potential solutions were provided.Moreover,this review pro-posed the perspective that realizing multi-function,recycling,and intensification should be the developing direction for future TWW treatment.This review is expected to provide a general guide for researchers who aspire to ameliorate TWW pollution problems and understand various methods utilized in this field.

Facile fabrication of functional cellulose paper with high-capacity immobilization of Ag nanoparticles for catalytic applications for tannery wastewater

It has been a research goal to develop macroscopic materials with an optimized surface structure to affix silver nanoparticles which could contaminate water and maximize their practical functions.Cellulose paper is a versatile biomass material valued for its abundance,low cost,biocompatibility,and natural composition.Until now,its potential application in water purification has not been adequately explored.In this study,gallic acid-modified silver nanoparticles(GA@AgNPs)were loaded onto commercial cellulose filter paper using a simple lipoic acid modification process(GA@AgNPs-LA-CP).Scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),and X-ray diffraction(XRD)were used to characterize the GA@AgNPs-LA-CP.The catalytic activity of the GA@AgNPs-LA-CP was evaluated by the reduction reaction of methylene blue(MB),Rhodamine B(RhB),and 4-nitrophenol(4-NP)with sodium borohydride(NaBH4).The GA@AgNPs-LA-CP exhibited excellent catalytic activity toward MB,RhB,and 4-NP,taking advantage of its high specific surface area generated by the cellulose fiber network structure.Interestingly,due to the electrostatic interactions between the cationic dyes and the GA@AgNPs,the as-prepared catalytic composite material serves as a better catalyst for MB and RhB,suggesting dual applications of the composite materials for organic wastewater treatment and the removal of harmful dyes.This implies that the immobilization of AgNPs on cellulose papers is an effective method and can be applied to efficient wastewater treatment applications.

Soil Explorations and Groundwater Monitoring to Evaluate Subsurface Contamination Due to Chromium in District Kasur, Pakistan

Due to improper tannery wastewater management in district Kasur Pakistan, groundwater has been reported to be highly contaminated. It was aimed to find out the extent up to which subsurface has contaminated due to chromium in areas adjacent to the tannery units. Eight （8） soil bores were conducted up to the depth of 30.5 meters and soil samples were tested for total and hexavalent chromium concentrations retained in soil by aqua regia digestion at the every depth of 1.5 meters. Afterwards monitoring wells were installed in these eight （8） bores so as to monitor chromium concentrations in the groundwater on monthly basis. The main source of contamination was considered to be the four （4） drains carrying tanneries effluent therefore samples were collected from these drains so as to observe seasonal variation in chromium concentration.