Anaerobic Biodegradation Of Coking Wastewater: Identifying The Characteristic And Impact Factors

The coking wastewater(CWW)produced in various coal chemical process is recognized as a kind of refractory wastewater,which contains high concentration and toxic organic compounds.Currently,A2/O,the most common bioprocess technology,is widely applied in the CWW treatment.Howerver,a series of full-scale practical applications of high concentration CWW anaerobic biological treatment have shown no success in generating CH4.Lacking the study about the anaerobic unit in the CWW treatment engineering,the mechanism influencing the activity of microorganism is indeterminate.As a result,in order to figure out thess problems,the raw CWW with COD of 4100±200 mg/L originating from the Shaogang coke production plant,Guangdong province,P.R.China,was studied for the factors inhibiting its anaerobic biodegradation,using the gradient dilution approach with the COD,TOC,phenol and bio-gas analyses.Concentrations of thiocyanide,phenol,sulfide,and cyanide were also considered as the limiting factors.The aberrance of anaerobic degradation performance,resulted from the changes with different carbon sources,were also studied.The main research contents and results are as follows:(1)The results showed satisfactory production of methane under the conditions of inoculated sludge at pH 7.0±0.5,35±0.5°C,and COD within the range of 1500-1800 mg/L.When three common industrial carbon sources,sodium acetate,glucose and methanol,were added to the CWW at concentrations equal to its COD of 2100 mg/L respectively,it indicated that hydrogenotrophic methanogens tolerate higher threshold value of toxicants than the acetate-utilizing methanogens.From the perspective of co-metabolism,the hydrolysis rate of phenol were enhanced and a mass of methane could be collected with the methanol biodegraded.From the aspect of energy recycling,a large amount of relative high-purity hydrogen was produced while glucose hydrolyzed,which might lay the basis for the research of biohydrogenlike technology on CWW.(2)As to CWW which is diluted to COD of 2100,2400 and 2700 mg/L with anaerobic biodegradation still restrained,methanol was used as carbon source for co-substrate degradation,and the effect of different methanol addition concentration and method on the promotion of pheonl hydrolysis was studied.The result revealed that when the specific value between CODCH3 OH and CODCWW ranged from 0.35 to 0.40 at one-off feeding mode with different concerntration of methanol on account of constant concentration of MLSS(5000 mg/L),the hydrolysis rate of phenol was the most satisfying while thiocyanide showed no performance on its co-substrate anaerobic biodegradation.By contrast,methanol added at batch feeding mode is 10-15% more efficient in phenol hydrolysis than that added in one-off way,and 15-25% more efficient than that without methanol.Therefore,the key promoting pheonl hydrolysis due to the effect of co-metabolism was that the microorganism produced key enzyme constantly.From the technical perspective,co-substrate anaerobic biodegradation could promote phenol hydrolysis in the CWW.However,in the practical engineering,its hydrolysis rate wasn't satisfying enough within limited HRT with cost-effectiveness analyses.(3)On the basis of low level of co-toxicity,the limiting concentrations of supplementary thiocyanide,phenol,sulfide and cyanide at the coking wastewater COD of 1800 mg/L ranged at 500-1500,1100-1250,200-250 and 30-40 mg/L,respectively.Besides,it suggested that the co-toxicity among them was expressed as the coupling synergistic effect through the evaluation of toxicity grading and it indicated that sulfide and cyanide were the main toxicant inhibiting anaerobic biodegradation for CWW.Furthermore,it would consume a volunm of acid to adjust the pH to the level which was suitable for anaerobic microorganism.Summarizing,difficult anaerobic biodegradation of high concentration CWW is enhanced by alleviating the inhibiting factors.To get satisfactory production of methane,lagre amounts of clean water would be needed,which was inconsistent with “Zero Emission”.Nevertheless,the efficiency of anaerobic biodegradation of CWW was disappointing without dilution,causing the uselessness of anaerobic unit in CWW treatment.For the sake of solving this contradiction,it is extremely necessary to identify the factors inhibiting anaerobic biodegradation for CWW.