Research On Purification Efficiency Of Simulated Marine Aquaculture Wastewater By Biofiltration System

Marine aquaculture industry is developing rapidly in coastal areas in China.The pollutants of aquaculture wastewater,like nitrogen,phosphorus,organic matter and suspended solids,remained to be purified to decrease coastal pollution load.Biofiltration is one kind of common technology for marine aquaculture wastewater treatment.Based on the characteristics of water quality,gravel-zeolite biofiltration system and zeolite-pyrite biofiltration system were set up and a filtration system for phosphorus removal was added.The research results are as follows:Heterotrophic denitrification-nitrification system was built with gravel and zeolite as filter media.The increase of salinity from 1% to 2% in start-up phase did not interfere in nitrification efficiency obviously.Glucose was used as external carbon source.When COD/TIN(total inorganic nitrogen)was 5.7,under different HRT(hydraulic retention time)conditions(12 h,24 h and 48 h)and different volumetric reflux ratio R conditions(50%,100% and 200%),HRT determined contact time and hydraulic load and further influenced nitrification efficiency,while R determined the content of nitrate and dissolved oxygen refluxed back to denitrification section and further influenced denitrification efficiency.When HRT was 24 h and R was 100% the results were better.Average removal efficiency of ammonia nitrogen and TIN was 91.8% and 66.6% respectively.The addition of carbon source did not cause secondary pollution,but the deficiency of carbon source was the main reason for limited TIN removal efficiency.Nitrification-autotrophic denitrification system was built with zeolite,pyrite and sulfur as filter media.Ammonia was mainly adsorbed by zeolite while phosphate was mainly adsorbed by pyrite.The adsorption capacity per unit empty volume of zeolite section and pyrite section was 1.68 g N/L and 0.092 g P/L respectively when salinity was zero.Ammonia adsorption capacity by zeolite section reduced by nearly 58% when salinity increased to 1.5%.Meanwhile,phosphate adsorption capacity by pyrite was hardly influenced by salinity.After successful start-up of the system,when HRT was 12 h,24 h and 48 h,average removal efficiency of ammonia was 95.0%,96.5% and 97.4% respectively and that of TIN was 86.1%,92.1% and 97.2% respectively.Nitrite did not accumulated.Produced sulfur compound existed as sulfate.The shortening of HRT may aggravate short-flow phenomenon.Systematic HRT had better be chosen as 24 h,9.6 h for zeolite section and 14.4 h for pyrite section.Prominent genera responsible for oxidizing ammonia and nitrite in zeolite section were Nitrosomonas and Nitrospira respectively.Prominent genus responsible for conducting sulfur autotrophic denitrification in pyrite section was Thiobacillus.Ferritrophicum,related to iron oxidizing bacterium,also coexisted.Phosphorus adsorption filter media was made from coal fly ash rich in Fe and Al(adsorption capacity 18.44 mg P/g)by adding quicklime as accessory ingredient and cement as hydrated agent.Under the condition of 40% water addition,the best ratio of coal fly ash,quicklime and cement was 21%: 0.5%: 38.5%.Continuous-flow experiment indicated that HRT of 16 h could satisfy the requirement of phosphorus removal.Average effluent phosphorus concentration was 0.04 mg/L.The probability of heavy metal release was low during the whole adsorption process.Long-term operation verified that zeolite-pyrite biofiltration was more suitable for purification for marine aquaculture wastewater.Effluent after treatment could meet the first-level standard of ?Discharge requirement for aquaculture wastewater‘(DB33/453-2006).