| According to the characteristics related to aquaculture, ex-suit biofloc technology(BFT) is exploited, which controls the conditions in the BFT reactor for the treatment of pollutants. BFT reactor could treat aquaculture wastewater and the effluents of recirculating aquaculture system(RAS). Ammonia(TAN) and nitrate(NO3--N) could be synchronously removed by BFT, and the nutritional composition of bioflocs can basically meet the demand of several kinds of aquaculture animal. This paper studied the efflects of distillery spent wash(DSW) addition and sludge retention time(SRT) on water treatment and the nutritional composition of bioflocs; a kind of BFT reactor, which was continuous flow, was designed and applied to a shallow raceway aquaculture systems and the effects of hydraulic retention time(HRT) on aquaculture wastewater treament was investigated.1. Nitrogen dynamics and bioflocs composition using biofloc technology to treat aquaculture solid waste mixed with distillery spent washDSW and aquaculture solid waste(ASW) were mixed homogeneously and used as substrate to produce bioflocs in reactors with biofloc technology. The added proportions of DSW(expressed as total chemical oxygen demand contents, COD), contributing to the total substrate content in the control group(GC) and treatment groups(G1/3 and G2/3) were 0, 1/3 and 2/3, respectively. The initial COD contents were statistically equal among all groups(5049.55±31.19 mg/L, 5035.87±106.04 mg/L and 5029.60±25.27 mg/L, respectively). During the experiment period, the nitrogen dynamics process was consistent among all groups, and a higher content of dissolved inorganic nitrogen and less total organic nitrogen accumulated in the treatment reactors than in the GC reactors. The nitrogen recycling rates for G2/3 was 44.19%, which was significantly less than that of G1/3(59.04%) and GC(69.67%) in turn. Bioflocs yields(considered as mixed liquor violate suspended solid, MLVSS) in G2/3 was 169.96 mg MLVSS/g COD, which was significantly less than that of G1/3(255.19 mg MLVSS/g COD) and GC(371.73 mg MLVSS/g COD). The higher proportion of DSW in the substrate was, the higher values of crude protein, crude lipid and ash in the bioflocs were. However, compared with the control and lower ratio of DSW(G1/3), higher addition of DSW(G2/3) decreased linoleic acid, linolenic acid, total polyunsaturated fatty acids(PUFA) and n-6 PUFA values. Besides, addition of DSW decreased the settling ability of the bioflocs.2. Effect of SRT on water quality, nutritional composition and apparent digestibility(AD) of bioflocs production from recirculating aquaculture system effluentsAs the assimilation of heterotrophic bacteria, nutrient of dissolved and solid fish waste can be converted into bioflocs, which can be re-utilized as aquaculture feed. In order to achieve the zero-emission of RAS and recycling of aquaculture waste, bioflocs was produced by BFT treating RAS effluents with sequencing batch reactors(SBRs). The effect of sludge retention time(SRT, 1 d, 2 d, 3 d, 4 d, 6 d and 8 d) on water quality and bioflocs nutritional composition were investigated. A kind of jellylike bioflocs pellet was designed and the apparent digestibility(AD) in tilapia(GIFT Oreochromis niloticus) was studied. The nitrification was inhanced with longer SRTs. The water quality of SBRs effluents, except NO2--N, was suitable to be reused for most aquatic animals. The protein content was increased firstly but later decreased with increasing SRT, and the highest level was obtained in the 3 d SRT bioflocs, i.e. 24.08 ± 0.94 % of dry weight. The lipid content was decreased from 3.52 ± 0.38 % to 3.00 ± 0.11 % with rising SRT(P>0.05).The bioflocs with 8 d SRT showed the highest linolenic acid concentration(20.95 ± 4.02 %) and the linoleic acid content was significant lower than that of 1 d SRT. The considerable dry matter AD, protein AD, crude lipid AD, crude ash AD and nitrogen AD of jellylike bioflocs pellet were 57.28-58.64 %(3 to 4 d SRT), 67.04-69.77 %(1 to 3 d SRT), 76.90-80.80 %(2 to 6 d SRT), 53.50-59.82 %(1 to 4 d SRT), 73.92-77.56 %(2 to 4 d SRT), respectively. The results indicate that BFT treating fish waste is important for the sustainable development of aquaculture, 3 d SRT is best for water treatment, nutritional composition and availability of bioflocs.3. The effects of HRT on aquaculture wastewater treament in a shallow raceway aquaculture systems based on BFT reactorA kind of BFT reactor, which was continuous flow, was designed and applied to a shallow raceway aquaculture systems in cuttent study. During the over-winter period for tilapia, the effectiveness of different hydraulic retention time(12 h, 6 h, 4.5 h, 3 h) on aquaculture wastewater treament was investigated. It indicated that the HRT of biofloc reactor could be as small as 4.5 h. An irreversible wash out phenomenon was observed during 3 h HRT, and the experiment could not continuously conducted. For 12 h, 6 h and 4.5 h HRT, the settling ability of bioflocs in reactive zone was generally satisfactory. Sludge volume index(SVI-30) was significantly decreasing with declined HRT, however, it was higher than 150 m L/g throughout the experiment. The waste removal rates(RR) in 12 h HRT were the highest. The lowest concentration of TAN, NO2--N, NO3--N and TN, SS in BFT reactor effluent were observed in 4.5 h HRT and 12 h HRT, respectively. These were 0.48±0.05 mg/L, 0.02±0.01 mg/L, 1.70±0.06 mg/L and 4.47±1.00 mg/L, 14±8 mg/L, respectively. The reactor could contain the concentration of TAN, NO2--N, NO3--N, SS on aquaculture zone lower than 1 mg/L, 0.2 mg/L, 3 mg/L, 40 mg/L, respectively. Numerous biflocs was harvested during the experiment period. The content of protein was significantly declined with decreasing HRT, crude lipid content was increasing with diminishing HRT. The contents of protein and crude lipid could as high as 31.01±0.62 % and 3.43±0.15 %, respectively. The results indicated that the HRT of biofloc reactor could as small as 4.5 h. The reactor was good for nitrogen waste and SS treatment, the best operational HRT was 4.5 h. |
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