Research On Saline Organic Wastewater Treatment With Anaerobic Membrane Bioreactor (AnMBR)

Saline organic wastewater was generated in industrial sectors such as food,printing and dyeing,medicine,chemical,and pesticide production.Without effective treatment,it will result in serious water pollution.Anaerobic biological treatment was considered as a promising method for treatment of organic wastewater for its advantages,such as high organic loading rate,high organic removal efficiency,and the energy recovery from wastewater through methanogenic process.However,the anaerobic treatment could be inhibited under high content of salt and lead to low organic removal efficiency.To clarify the inhibition mechanism,and find a suitable method for reliving the inhibition effect and improve the organic removal efficiency is still vital problem to be resolved in the practical saline organic wastewater treatment engineering.Therefore,the effect of salt on anaerobic biological treatment system was evaluated,and the stress effect of salt on anaerobic system was discussed in this study.The differences of microbial community structure and microbial activity under different salt stress conditions,and moreover the response of anaerobes to sodium stress were investigated by using of high throughput sequencing and flow cytometry technology.The changes of metabolites,extracellular polymers and enzyme activities of microorganisms under different concentrations of sodium were studied.KCl was selected as external osmolytes for enhancing the effect of anaerobic biological treatment,and the regulation mechanism of adding KCl to improve the resistance of anaerobic bacteria to high osmotic pressure was analyzed.Finally,an anaerobic membrane bioreactor?AnMBR?with polytetrafluoroethylene?PTFE?hollow membranes was constructed for retaining anaerobic microorganism and improving saline organic wastewater anaerobic treatment efficiency based on the combination of anaerobic biotechnology and membrane technology.The performance of AnMBR for treating saline organic wastewater was evaluated,and further the fouling characteristics and cleaning methods of PTFE hollow fiber membrane in AnMBR were studied.The results are as follows:?1?The anaerobic digestion performance of saline organic wastewater with different salt content was evaluated.It showed that,the mesophilic anaerobic digestion could be operated when salt conent was 10.6g/L,and under this condition,the organic removal rate was 82.5%,and the chromaticity of the effluent was 50,which was caused by the exudation of intracellular substances,such as protein-like and humic acids-like substances.When the salt concentration reached 42.4 mg/L,the anaerobic performance deteriorated sharply,and the organics removal rate dropped to 35.6%.High salt concentration had different effect on different phases of anaerobic digestion,and especially it had a significant negative impact on the methane production phase,and which resulted in the accumulation of volatile fatty acids?VFAs?in the anaerobic reactor.The high accumulation of acetate,propionate and butyrate was observed when the salt contents were 26.5 g/L,42.4 g/L,and 63.6 g/L,respectively.High content of salt showed relatively low impact on hydrolysis/acidification phases,and the methane-production phase is the restrictive process of anaerobic digestion under the condition with high content of salt.?2?The response of anaerobic microorganism to sodium ion stress was studied.The particle size of anaerobic sludge was correlated with the salt concentration negatively.As the sodium ion concentration was 1.2 mol/L,the average anaerobic sludge particle size decreased by 26.4%compared with the sludge under normal condition.The decrease of average particle size of sludge was probably caused by the increase of protein proportion with small molecules less than 350 Da in EPS under the condition of high osmotic pressure.Salt concentration also affect the pentose phosphate pathway during anaerobic digestion.High concentration of 6-phosphogluconate dehydrogenase is required so as to maintain the normal pentose phosphate pathway.The overall activity of anaerobic bacteria was negatively correlated with sodium concentration.When sodium concentration was 0.2 mol/L,0.5 mol/L,0.8 mol/L,and 1.2 mol/L,the proportion of apoptotic cells was 60.6%,73.7%,88.3%and 90.3%,respectively.?3?For the anaerobic digestion of organic wastewater with 20.0 g/L of NaCl,the addition of KCl promoted the anaerobic biogas production to the greatest extent when KCl content was0.17%.Under this condition,the COD removal rate was 62.7%,which was 115.4%higher than the anaerobic digestion system without KCl addition.Appropriate dosage of KCl can promote the degradation of protein and humic acid-like substances during anaerobic digestion,and maintain the dehydrogenase activity of anaerobic microorganisms.The filamentous bacteria was more susceptible to salt stress,however,the addition of KCl can improve the salt tolerance of filamentous bacteria under high salt stress,and meanwhile maintain the morphology of anaerobic globular bacteria.?4?PTFE hollow fiber membrane AnMBR was used to treat saline organic wastewater.When the salt content increased from 11.0 g/L to 19.0 g/L,27.0 g/L,and 35.5 g/L,the biological COD removal rate decreased while the COD removal rate by PTFE membrane filtration increased,and the total COD removal rate kept stable.Finally,after the filtration by PTFE membrane,the COD of the effluent of AnMBR was 549.0 mg/L,and the total COD removal efficiency was 97.2%.The biological COD removal rate was 95.5%-89.9%as the salt content increased,the high organics removal efficiency was due to the retention effect of PTFE hollow fiber membrane on microorganisms,and lead to the accumulation of Proteobacteria and Bacteroidetes,which were known as salt tolerant microorganisms,and their relative abundances were 35.7%and 25.9%.Therefore,AnMBR exhibited excellent performance for saline organic wastewater treatment.?5?PTFE hollow fiber membrane AnMBR was used to treat saline organic wastewater with different salt content,and the fouling characteristics of PTFE hollow fiber membrane and the cleaning effect was investigated under constant membrane flux.The membrane resistance growth rate of PTFE hollow fiber membrane increased from 1.88×10¹¹/?m·d?to 2.63×10¹¹/?m·d?when the salt content increased from 11.0 g/L to 35.5 g/L,which means higher salt content accelerated membrane fouling.However,the irreversible membrane fouling effect was almost the same.When the fouled PTFE hollow fiber membrane was cleaned with tap water,sodium hydroxide solution?2.0%?,and hydrochloric acid?1.5%?for 10 min,the recovery rate of membrane flux reached 92.3%-96.5%.PTFE hollow fiber membrane is an ideal membrane material for AnMBR in treating saline organic wastewater.