Performance And Mechanism Of Anaerobic Biodegeradation Of Formaldehyde In Industrial Wastewater At The Presence Of Different Co-substrates

Petrochemical industry has contributed greatly to the development of society,while the petrochemical wastewater produced during the manufacture process of various chemicals have also polluted the water bodies greatly.Petrochemical wastewater like Trimethylolpropane?TMP?wastewater contains high-strength formaldehyde?FA?,which is highly toxic and pose great threat to microorganisms and human.The mainstream technology for treating high-FA-containing wastewater is the oxidation method,advanced oxidation method in particular,which requires complicated controlling and costs too much.The anaerobic biodegradation of FA with five common carbon sources including glucose?G?,sodium acetate?SA?,sodium propionate?SP?,methanol?M?and ethanol?E?was investigated systematically.Based on the two-phase anaerobic digestion,the toxicity of simulated FA wastewater and TMP wastewater to the specific acidogenic activity?SAA?and specific methanogenic activity?SMA?was discussed and related.The main conclusions are as follows:1.The simulated FA?SFA?wastewater and TMP wastewater are highly toxic to the microorganisms in acidogenic phase and methanogenic phase.The 50%inhibition concentration(EC₅₀)of SFA and TMP wastewater to SAA was 174.48 mg/L and 94.23mg/L,respectively;and their EC₅₀ to SMA was 94.53 mg/L and 87.66 mg/L,respectively.Formaldehyde was the main toxicant in TMP wastewater that caused toxic effect to SAA and SMA.2.The optimum conditions for anaerobic degradation of FA in acidogenic phase was at the sludge concentration of 3 g VSS/L and with the SA concentration of 1.5 g COD/L.The increase or decrease FA biodegradation rate by the addition of five carbon sources was initial FA concentration-dependent.At FA concentration?120 mg/L,SA and E could promote FA degradation rate which was increased slightly by 4.9%-17.7%;when FA concentration was from 200 to 1000 mg/L,all five substrates could promote the FA degradation rate and they were in the order of SA?18.07-52.17%?>SP?13.2-49.9%?>E?24.6-44.1%?>G?11.22-31.3%?>M?9.3-17.7%??3.The optimum conditions for anaerobic degradation of FA in methanogenic phase was also at the sludge concentration of 3 g VSS/L and with the SA concentration of 1.5g COD/L.The increase or decrease of FA biodegradation rate by the addition of five carbon sources was also initial FA concentration-dependent.At FA concentration?200mg/L,only three substrates could promote FA degradation rate,and they were in the order of SA?35.1-45.7%?>SP?22.8-36.9%?>G?15.3-21.6%?.When the formaldehyde concentration is 400 and 1000 mg/L,only SA and SP could promote FA degradation rate slightly.4.The addition of co-substrates under anaerobic conditions can promote the degradation rate of FA in TMP wastewater,and it was increased by 3.8-56.4%and11.45-29.1%by the G and SA in the acidogenic and methanogenic phase,respectively.5.After exposure to toxic substances,microorganisms could produce more EPS and protect themselves against the toxicity.Within a certain range of FA concentration?0-200 mg/L?,the presence of the co-substrates could protect the microorganisms against the toxicity;however,if the FA concentration continues to increase,the microorganisms will still be greatly poisoned.6.With or without G as the co-substrates,the FA could be removed by over 97%at influent FA?1360 mg/L.FA could be transformed into methanol and acetic acid.The presence of G could lead to the production of propionic acid and butyrate.7.The microbial results indicated that with the increase of FA and organic loads,the Firmicutes,Bacteroidetes,Chloroflexi and Proteobacteria were the dominant phylum.The distinct compositon of microflras on genus level corresponded to the different performance of two EGSBs.