Study On Treatment Of Seafood Wastewater Using Anaerobic Digestion,Coagulation And SNAD Process

In recent years,with the gradual increase in the import and export of seafood,the amount of wastewater generated by the processing of seafood has also increased.In the processing of seafood,a large amount of wastewater is generated in the processes of cooking,washing,thawing,and waterretention agent soaking.Due to the addition of waterretention agent and soaking of meat products,the wastewater in the water-retaining process contains high concentration of COD,organic nitrogen and polymeric phosphates.In this paper,the anaerobic digestion-coagulation-SNAD combined process,was designed to reduce carbon,nitrogen and phosphorus in the wastewater,aiming at reducing the subse quent biological treatment load.Firstly,the wastewater in the water retention workshop is pretreated.The anaerobic digestion reactor was started stably with wastewater.The COD removal effect and the conversion effect of nitrogen and phosphorus in the reactor were analyzed,and the High-throughput sequencing analysis of the reactor sludge before and after the operation of the wastewater was carried out.Secondly,after anaerobic digestion,Chemical coagulation removes high concentrations of phosphate from wastewater.At the same time,the SNAD process was started with simulated wastewater,and the operating parameters of the reactor were determined.The pretreated wastewater from the water retention workshop was denitrified by the SNAD process.The conclusions reached are as follows.?1?The anaerobic digestion reactor was successfully started for a total of 86 days.In stable operation,the maximum influent volume load is 7.8 kg COD/?m³·d?,the COD concentration can be reduced to 439.12 mg/L,the removal rate is maintained above 90%,and the effluent COD concentration is stable at 300-500 mg/L.After anaerobic digestion,the concentrations of NH₄⁺-N and PO₄^3--P reached 85-90%of total nitrogen and total phosphorus,respectively.The presence of organic substances such as proteins in the wastewater caused Thermovirga bacteria to be present in the reactor,which the content was 14.53%.The competition of Thermovirga against the substrate was observed.It may be the reason that the Rikenellaceae in the original sludge was eliminated.?2?During chemical coagulation process,with the conditions of rapid stirring?180 r/min?for 1 h,adding 1 mL of PAM then slowly stir?80 r/min?for 30 min,there has the best effect of removing phosphorus,at mass ratiom _{polyaluminumchloride}:m _sepiolite=10:3.The flocculated precipitates formed is CaAl₃?PO₃OH?SiO₃,respectively.The concentration of orthophosphate in the wastewater after coagulation can be reduced from 1000.14 mg/L to 1.70 mg/L.The average concentration of phosphate in the effluent is 6.59 mg/L,and the removal rate of phosphorus is 99.06%on average,up to 99.83%.?3?The artificial simulated wastewater is stably started in the SNAD process at a temperature of 32-35?,intermittent aeration of 10-40 mL/min for 10 h?Tae:Tan=10 min/5min?,and the influent pH is about 8.Under the highest stable treatment,the influent nitrogen load is 1.14 kg N/?m³·d?,and the TN removal rate can reach 75.34%.The COD removal rate can reach 50.78%,and the nitrogen removal rate is 0.86 kg N/?m³·d?.The wastewater of the water retention workshop was treated with the reactor parameters when the simulated wastewater was operated.The removal rates of total nitrogen and COD in the SNAD process were 71.37%and 69.80%,respectively.High-throughput sequencing results indicated that the SNAD system was formed in the reactor,and the contents of AOB,AnAOB and DNB were2.72%,2.09%and 1.46%,respectively.