The Initial Study On Anaerobic Digestion Of Biosoilds From Recirculating Aquaculture System By Anaerobic Sequencing Batch Reactor

In intensive aquaculture condition, the cultured population produce a great amout of sludge, be mainly composed of uneaten feed and excreta.The common solids managements include composting, landfill and so on, however, these actions are harmful to the environment, especially the salty solids need effective pretreatment in order to reduce the negative effect. Anaerobic digestion can decompose the organic matter and produce biogas with the result of minimization and stabilization.Laboratory experiment was conducted to investigate the feasibility and performance of an anaerobic sequencing batch reactor (ASBR) at 35±1℃and 20 days hydraulic retention time(HRT)for the digestion of biosolids(remnant feed and feces) generating from the recirculating aquaculture system (RAS).The experiment of start-up period results indicated that from day 53rd to 59th, the"wash out"of sludge from the system leaded to the variation of effluent. The pH value was stable in 7.01-7.45 during the whole operation, the VSS/SS of sludge within the system was increased from 29.28% when inoculated to 44.12% finally. On day 117th the system began to produce biogas, gas yields between 0.013 and 0.022 l/g COD added were achieved. The digested sludge with the volume reduction of 93.75% and stabilization of 41.61% in terms of VSS/SS comparing to the raw sludge were attained.Remain the aforementioned reaction conditions, applying the method of salinity acclimatization to structure the anaerobic system which could dispose of salty biosolids generating from RAS (Influent loading: COD:7.8-8.2g/l, TSS: 4.19-6.52 g/l, VSS:1.14-2.28 g/l) on the basis of the above launched ASBR. The experiment lasted 75days and the results showed that: the biogas production went down with the increase of salinity, between day 35-43, and day 61-75,the system was unable to produce biogas, the mean biogas production was between 0.0167-0.0176 l/g COD in the aerogenesis phase. The effluent concentration of PO₄^3--P was fluctuating down, while TAN and SCOD were fluctuating up.When the system salinity was 6, the effluent concentrations of PO₄^3--P ,TAN and SCOD were fluctuating irregularly. The effluent about pH value was fluctuating between 6.38-7.45, and the alkalinity rose from 900mg/l to1700.2mg/l. The SVI within the system went up from 32.42ml/g to 45.79ml/g with the increase of salinity.The further study had tested the performance of anaerobic system by applying addition carbon source and ultrasonic pretreatment in order to offer reference for how to enhance the biogas production on the basis of the system which underwent salinity acclimatization with the final salinity was 10.46.The experiment results demonstrated: in the initial start-up period, the system did not produce biogas. In the addition carbon source phase , the system began to produce biogas and the production was between 0.08-0.02 l/g TCOD ,went up along with the increasement of carbon source. When stopped addition, the biogas production went down markedly. In the ultrasonic pretreatment period, the biogas production increased, the amount was between 0.015-0.022 l/g TCOD .The effluent of pH value decreased with the addition of carbon source, went down from 6.73 to 6.37, and alkalinity declined from 2099.6 mg/l to1607.11 mg/l while without the carbon source addition , pH value increased, and the alkalinity rose to 2616.11 mg/l. In the ultrasonic period, the alkalinity dropped to 2007 mg/l.In the addition of carbon source phase, the effluent concentration of SCOD turned down from 938-280 mg/l , PO₄^3--P dropped from 28.43 -22.47 mg/l , TAN was fluctuating between 126.92 and 589.6 mg/l . Without carbon source addition, SCOD went up slowly, PO₄^3--P went up from 22.47 mg/l to 36.38 mg/l, TAN went up from 128.74-289.32mg/l. In the ultrasonic pretreatment phase, the concentration of SCOD increased from 170 mg/l to 680 mg/l, PO₄^3--P went up from 23.71-31.16 mg/l while went down from 84.03-79.47mg/l.The addition of carbon source could effectively stimulate the growth of microbes, however, it gave rise to large loading pressure to the anaerobic system and had the risk of leading to operation failure.The ultrasonic pretreatment can decompose the biosolds effectively and accelerate the hydrolyzation, so was beneficial to anaerobic digestion.