Using a Statistical Model to Examine the Effect of COD: SO42− Ratio, HRT and LA Concentration on Sulfate Reduction in an Anaerobic Sequencing Batch Reactor

Real effluents and fractionation in the supply of COD: Rapid adaptation and high efficiency to treat mine drainage combined with industrial by-products

The biological treatment of mine drainage (MD) using sulfate-reducing bacteria (SRB) is a technology in growing exploitation. The use of by-products as sources of electrons can make this treatment more environmentally and economically advantageous. However, the high chemical oxygen demand (COD) and the presence of recalcitrant molecules can lead to the accumulation of metabolic intermediates that acidify the system, thus interrupting the treatment. Besides, the adaptation of the inoculum to the establishment of sulfidogenesis with MD and by-product may be slow. This study aimed to investigate prompt adaptation and operation strategies that do not require additives to enable the sulfidogenic process to occur while maintaining a pH close to neutrality. The sources of electrons tested were trub (brewery residue) and crude glycerol - CG (residue from the biodiesel production). The inoculum from a methanogenic reactor was stored with a real MD for a month. The adapted inoculum was applied in a batch reactor for 168 h of hydraulic detention time, and promoted 75.8 ± 4.3% of sulfate removal from an MD with 3756.4 ± 258 mg.L^-1 of sulfate using CG in a COD/SO₄^2- ratio of 3 ratio. With higher initial substrate concentrations, acidification occurred and the treatment was interrupted. Using trub instead of CG, the acidification occurred at a COD/SO₄^2- ratio of 3. Acidification was prevented and the best efficiencies in sulfate removal were obtained when the amount of substrate corresponding to COD/SO₄^2- ratio of 3 was fractioned into equal parts and added over six days in the CG reactor. It was achieved 94.15 ± 1.76% of sulfate removal. With trub, the same procedure in which this COD was divided into seven parts, and resulted in a sulfate removal of 88.49 ± 1.02%. The removal of metals and metalloids were greater than 94.5% in all the systems in which the substrate supply was made fractionally, and the effluent generated presented alkalinity between 3370 and 4242 mg CaCO₃.L^-1, and pH between 6.8 and 7. The method of adaptation and operation applied allowed the realization of a MD treatment with quick establishment of sulfidogenesis and without the use of neutralizing additives. Finally, the effluent presented characteristics considered favorable for a later stage of post-treatment of the effluent with methane generation.

Anaerobic digestion of sulphate-rich post-tanning wastewater at different COD/sulphate and F/M ratios

Anaerobic digestion of post-tanning wastewater was performed in batch anaerobic digester to evaluate the effect of COD/sulphate ratio [0.62, 0.69, and 1.20 (w/w) %] and F/M ratio [0.2, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, and 1.5 (w/w) %)] on the removal efficiency of COD. The F/M ratio of 0.3 was found to be the optimum ratio for the removal of COD by 53, 57, and 65%, respectively at COD/sulphate ratio of 0.62, 0.69, and 1.20. The maximum sulphate removal was observed at F/M ratio of 0.2 and the removal efficiency was 48, 50, and 58% at COD/sulphate ratio of 0.62, 0.69, and 1.20, respectively. The removal efficiency of COD and sulphate was increased with increase in COD/sulphate ratio from 0.62 to 1.20 and decreased with increase in F/M ratio from 0.2 to 1.5 in anaerobic digestion of post-tanning wastewater. The maximum concentration of sulphide formation was 784 mg/L at COD/sulphate ratio of 0.62 in anaerobic digestion process and the process was inhibited at this sulphide concentration. The microbial activity in the sludge was evaluated through live and dead cell assay using fluorescent microscopy. The maximum amount of dead microbes was observed in the anaerobic digester, which was operated at COD/sulphate ratio of 0.62 than other studied ratio.

Optimization of the operation of packed bed bioreactor to improve the sulfate and metal removal from acid mine drainage

The present study discusses the potentiality of using anaerobic Packed Bed Bioreactor (PBR) for the treatment of acid mine drainage (AMD). The multiple process parameters such as pH, hydraulic retention time (HRT), concentration of marine waste extract (MWE), total organic carbon (TOC) and sulfate were optimized together using Taguchi design. The order of influence of the parameters towards biological sulfate reduction was found to be pH > MWE > sulfate > HRT > TOC. At optimized conditions (pH - 7, 20% (v/v) MWE, 1500 mg/L sulfate, 48 h HRT and 2300 mg/L TOC), 98.3% and 95% sulfate at a rate of 769.7 mg/L/d. and 732.1 mg/L/d. was removed from the AMD collected from coal and metal mine, respectively. Efficiency of metal removal (Fe, Cu, Zn, Mg and Ni) was in the range of 94-98%. The levels of contaminants in the treated effluent were below the minimum permissible limits of industrial discharge as proposed by Bureau of Indian Standards (IS 2490:1981). The present study establishes the optimized conditions for PBR operation to completely remove sulfate and metal removal from AMD at high rate. The study also creates the future scope to develop an efficient treatment process for sulfate and metal-rich mine wastewater in a large scale.