Detoxification Process And Mechanism In Hydrolysis Acidification Pretreatment For Trimethylolpropane Wastewater

Trimethylolpropane(TMP)wastewater is widely known for the high-concentration of organics and high toxicity to microorganisms in biotreatment processes.This study aims to analyze the toxicity,the composition and the key toxicants of TMP wastewater,and investigate the toxicity removal effect and mechanisms of hydrolysis acidification(HA)as the pretreatment of TMP wastewater.Oxygen uptake rate(OUR)test,anaerobic toxicity assay(ATA)and luminescent bacteria test(LBT)were used to determine the toxicity to biotreatment of TMP wastewater.The concentrations that inhibited the oxygen uptake rate,the specific methane yield and the luminescence by 50%were 761,1347 and 171 mg COD/L,respectively.These results indicated that TMP wastewater cannot be directly treated by aerobic activated sludge or used for anaerobic methane production.Analytical method was developed for the specific organic substances in TMP wastewater.A total of 19substances in TMP wastewater were quantified simultaneously after optimization of parameters in pretreatment and chromatographic conditions.The intraday and interday precision of each substance were below 1.66%and 14.07%,respectively.The detection limit and quantitation limit of the analytical method were 0.02~6.22?g/L and 0.07~20.72?g/L,respectively.The toxicity of TMP wastewater could be removed efficiently by HA process.Toxicity of TMP wastewater assessed by OUR could be completely eliminated with the organic loading rate(OLR)less than 7.5 kg COD/(m~3·d).Even with the OLR up to 9 kg COD/(m~3·d),the inhibitory ratio of OUR could still be decreased from 100%to 34.9%.Besides,COD and TOC could also be removed by 24.9±5.9%and 41.8±4.4%,respectively.The results indicated that by HA process the toxicity to biotreatment of TMP wastewater could be reduced more effectively than the regular water quality indices.During the operation of the process,Firmicutes,Bacteroidetes and Chloroflexi gradually became the dominant phyla.The proliferation of Firmicutes was presumably related to the stability of HA reactor.According to the removal efficiency of TMP wastewater toxicity,the operational parameters of HA were optimized as follows:HRT of 24 h,reflux ratio of 20:1 and the pH of raw water unadjusted.Under these conditions,the toxicity of TMP wastewater assessed by both OUR and ATA was removed completely,and the toxicity unit of LBT was decreased significantly from 0.58 to 0.04.Formaldehyde in TMP wastewater was identified as the main contributor to the toxicity of TMP wastewater according to the results of substance analysis and toxicity assessment.The change trend of formaldehyde concentration with time in TMP wastewater was in accordance with that in the artificial formaldehyde solution prepared at the original concentration of formaldehyde in TMP wastewater.This indicated that the degradation of formaldehyde in TMP wastewater was not disturbed obviously by other substances in the wastewater.After the treatment by HA,the effluent was diluted for biodegradability evaluation.When the effluent of HA was diluted,the aerobic degradation rate could reach 99%,and the biodegradation rate by anaerobic methanogenic bacteria could reach up to 71.5%.In conclusion,HA as the pretreatment technology,could be successfully applied for the toxicity removal of TMP wastewater,which guaranteed the stability of subsequent biological processing units.