Treatment Of Synthetic Mariculture Wastewater By Biological Filtration Process

Mariculture has become an important source of protein in the world. With the increase of aquaculture scale and strength, the development of mariculture has becoming more and more large-scale and industrialized, wastewater has the characteristics of large amount in volume, high strength in concentration and difficult to control. Massive mariculture wastewater released into the sea water will lead to the seawater nutrient salt content increased rapidly, thus promoting the abnormal reproduction of algae, consequently followed by the frequent occurrence of red tide, damage on species diversity, and another serious issues of the marine environment.Therefore, a series of bench-scale tests were conducted in this study to investigate the ammonia adsorptive property of inartificial media(such as zeolite, volcanic and ceramic) under various salinity based on the characteristics of mariculture wastewater. Considering economic cost, zeolite was finally chose as the best media to continue further study. By inoculating different seed sludge, the start-up phase and operating phase of zeolite biological filter with diverse salinity were surveyed. Once stable operation was gained, processing performance under different working conditions were explored, and structure change of system's microorganism population structure were demonstrated using PCR-DGGE and another molecular biological techniques.The results of the study indicated that the adsorption capacity of the filter was reducing with the salinity increasing in biological filter(zeolite, volcanic, and ceramic) adsorption performance experiments, and the adsorption equilibrium time was prolonged with zeolite extending from 50 min to 90 min, volcanic extending from 30 min to 80 min, and ceramic extending from 20 min to 90 min. The adsorption effect of zeolite was still better than that of volcanic and ceramic. When salinity was 0g/L, ammonia adsorption isotherm all the three media were in accordance with the Freundlich equation, which indicated that besides monolayer adsorption there was also multilayer adsorption in them. While salinity was 30g/L, there were still both monolayer adsorption and multilayer adsorption in zeolite and volcanic, whereas there was only monolayer adsorption in ceramic. The adsorption kinetics of three media for ammonia adsorption could be represented by the pseudo-second-order kinetics model when salinity was 0g/L and 30g/L, respectively. All the results showed that zeolite has better ammonia adsorption efficiency than volcanic and ceramic in the given salinities. Therefore, the selection of zeolite was the main research object in the follow-up study.With the stable influent condition of 30g/L salinity, marine sediment sludge and conventional activated sludge were severally inoculated to the 1# and 2# biological filters. It came out that the two filters cost 39 days and 35 days for the establishment, respectively, and the effluent quality of 2# was better than that of 1#. With the gradually increased salinity(from 0g/L to 30g/L), the establishment of 3#(inoculated with marine sediment sludge) and 4#(inoculated with conventional activated sludge) severally cost 60 days and 65 days, and the effluent quality of 3# was better than that of 4#. Taking the above results into consideration, it demonstrated that there was little influence in the starting time whatever sludge was inoculated, but it saved reactor start-up time efficiently to establish the biological filters directly under high salinity, and it was good for the domestication and enrichment of salt-tolerant and halophilic microorganisms.With hydraulic retention time(HRT), air-water and temperature ratio were severally30 min, 3:1 and 20 ? under stable operating conditions, the effect of biological filter on the removal of pollutants in the stable operation stage was investigated. The results showed that the average removal rates of 1#, 2#, 3# and 4# biological filters were 91%, 95.7%, 96.5%, 88.1% in ammonia nitrogen, the average removal rate of nitrite nitrogen were 89.2%, 94.8%, 97.2% and 84.9%, respectively, and the average removal of permanganate index(CODMn) were 49.86%, 53.9%, 54.5% and 48.1%.In the given range of test temperature, the removal efficiency of ammonia nitrogen and permanganate index by the biological filter show a gradually increasing tendency along with the temperature increasing. The removal of ammonia nitrogen and potassium permanganate index in the biological filters were investigated under various gas water ratio and hydraulic residence time. Considering economic costs and processing efficiency in practical engineering, the best gas water ratio was determined as 3:1, and optimal hydraulic retention time was 30 min, under which conditions ammonia concentration of the effluent can meet the discharge requirements of mariculture wastewater. The romval of ammonia and CODMn stayed steady even under ammonia shock, which indicated that the biological filter were resistant capacity to ammonia shock. And with increasing organic shock load, the removal rate of CODMn still increased gradually, while ammonia removal rate was decreasing, owing to the competition of dissolved oxygen, and nutrient competition between nitrifying bacteria and heterotrophic bacteria, thus affecting the rate of nitrification.Analysis results molecular biology demonstrated that the abundance of microorganisms in all the four biological filters were good after 30 days of the establishment, disregarding variation in influent conditions, and the Shannon diversity index of samples in 1#, 2#,3#, and 4# biological filters were 2.65, 2.88, 2.84, and 2.85, respectively. According to the analysis of species similarity, the analysis on biological population similarity showed that the impact of inoculated sludge on the bacterial communities was less than that of the starting method.After 30 days of the establishment under the condition of starting the biological filters directly with 30g/L salinity salinity, dominant species in the systems mainly include Alphaproteobacteria in Proteobacteria, Betaproteobacteria, Flavobacterium in Bacteroidetes and Bacilli in Firmicutes. And after 30 days of the establishment under the condition of starting the biological filters with gradually increased salinity, dominant populations involve Oceanospirillales and Nitrobacterin in the ?-Proteobacteria, Flavobacteriia in Bacteroidetes, Bacilli and Clostridia in Firmicutes.