Areca-cooking Wastewater Treatment Using A Combined Aluminum-carbon Micro-electrolysis-Coagulating Sedimentation-EGSB-SBR System

Areca-cooking wastewater is a kind of intractable organic acid wastewater with high COD and high colority. At present, special studies on areca-cooking wastewater treatment have not been reported in the domestic and foreign research. There is sporadic coverage of treatment for comprehensive wastewater from areca processing. However, extensive application was hindered by complicated operation and extraordinary cost in areca processing wastewater treatment. In this research, based on the principle of separate wastewater treatment according to wastewater quality and flow, areca-cooking wastewater was treated by a combined aluminum-carbon micro-electrolysis-coagulating sedimentation-EGSB-SBR system. The optimum operation parameters of each technology unit of the new combined system were confirmed by the experiment in order to provide new ideas and design basis.Areca-cooking wastewater was pretreated by aluminum-carbon micro-electrolysis. When the initial pH value, colority, SS and COD index of the areca-cooking wastewater was3.5,1000(times),647mg·L-1and14688mg·L-1, respectively, the results of orthogonal experiments and single factor experiments showed that the order of different factors and optimal operating parameters of micro-electrolysis method were as follows:dosage of aluminum shavings> mass ratio of aluminum to carbon> reaction time> initial pH value; the dosage of aluminum shavings was70g·L-1, the mass ratio of aluminum to carbon was1:1.5, and the reaction time was240min. The average removal rate of colority, SS and COD index were87.5%,97.2%and53.8%, respectively, in the optimal operating parameters, and the biodegradability (BOD5/COD ratio) of the wastewater was improved from0.28to0.68so that it set up the appropriate foundation for the sequent biochemical treatment. Components of pollutants of wastewater before and after treatment were analyzed by UHPLC-Q-TOF/MS. The results showed improving biodegradability of areca cooking wastewater might be related to removal of non-biodegradable plant phenols, they might be removed by aluminum-carbon micro-electrolysis with deoxidization, complexation, flocculation, adsorption, coprecipitation and electrophoresis. After aluminum-carbon micro-electrolysis treatment, coagulating sedimentation was used for enhanced treatment of areca-cooking wastewater. When the initial pH value, colority, COD index, turbidity and aluminum concentration of the influent were4.09,375(times),9500mg·L-1,460.0NTU and206.405mg·L-1, respectively, colority, COD index, turbidity and aluminum concentration of the effluent after treatment were125(times),6750mg·L-1,8.3NTU and12.621mg·L-1, respectively, and the corresponding average removal rate were66.7%,28.9%,98.2%and93.9%, respectively. Not only were colority and COD partially removed by coagulating sedimentation, but also turbidity and aluminum concentration were removed. So that it set up the appropriate foundation for the sequent biochemical treatment.After areca-cooking wastewater treated by aluminum-carbon micro-electrolysis and coagulating sedimentation, its biodegradability was improved.In the medium temperature (35±1℃), the areca-cooking wastewater was treated by EGSB anaerobic reactor. When the hydraulic retention time (HRT) was1day, COD index declined from6895mg· L-1to857mg·L-1and COD removal efficiency was87.6%in volume load6.9kg COD/(m3·d). When HRT was5days, COD index declined from6895mg·L-1to357mg·L-1and COD removal efficiency was94.8%in volume load1.4kg COD/(m3·d); however, NH3-N index of the effluent increased from3.4mg·L-1to120.5mg·L-1. Considering the performance of the EGSB anaerobic reactor and the follow-up aerobic process, the optimum HRT of EGSB anaerobic reactor was1day.After being treated by aluminum-carbon micro-electrolysis, coagulating sedimentation and the EGSB anaerobic reactor, COD index of the areca-cooking wastewater greatly reduced, but NH3-N index of the effluent significantly increased so that it could not meet wastewater discharge standard. The wastewater was treated by pre-denitrification SBR to meet the discharge standard. The results showed that optimal operating parameters were as follows: volume exchange ratio of SBR reactor was1:2and operating conditions of SBR reactor were influent Oh, anoxic phase2h, aerobic phase8h, settle1h, drawn Oh. When the initial pH value, colority, COD index and NH3-N index of the influent were7.95,100(times),837mg·L-1and86.2mg·L-1, respectively, the colority, COD index and NH3-N index of the effluent were32(times),75.1mg·L-1and4.54mg·L-1, respectively.Aluminum-carbon micro-electrolysis-coagulating sedimentation-EGSB-SBR combined system for areca-cooking wastewater treatment has technical reliability and economic feasibility. On one hand, water quality indexes of the final effluent were under the first-class of Integrated Wastewater Discharge Standard (GB8978-1996). On the other hand, Aluminum-carbon micro-electrolysis, key technology of combined system, features low cost and easy operation, compared to the developed and prevalent Fenton advanced oxidation technology for areca-cooking wastewater treatment.