| Along with Chinese economic development, human population growth and rised quality protein requirement, the scale of aquaculture and fish processing industry were increased quickly. However, due to the complicated reasons of processing technology, production cost and even the economic structure, the treating situation of the aquatic wastewater was grim. Thus it should be reckoned with the according environmental influence earnestly.Based on the conventional wastewater treatment technology, the organics, nitrogen and phosphorus were considered as contaminants, and then removed out of the system. This operated strategy were not only faced the sludge disposal costs, but also the sustainability were worth consideration. Due to the wastewater substrate were from the feed and breeding species themselves, and have well biodegradability, the bio-flocs technology were used for the treatment and recycling, which through for the increased process assimilation, and the proliferous heterotrophic bacterias catched by the cultured objects again. Nevertheless, due to several technological barriers, such as wastewater characteristics complexity, unsuited C/N/P ratio, and confining process control et al, the current operated practice were still faced with unstable system performance, high organics supplied cost and the low universality of the technology application. The focus was main in flocs production and aquaculture requirement, comprehensive wastewater treatment performance was neglected. Thus, research and development of the improved processing technology through bio-flocs technology for aquaculture and fish processing wastewater were very urgent for the dual purposes of the flocs production and treating performance.According of the above problems, the thesis was focus in the reasonable distribution of the limited substrate, which for the purpose of improved utilization efficiency of the internal carbon source, to diversify the substances utilization pathway and flocs PHB enrichment.Under laboratory and pilot scale, several research were carried out for the aquatic wastewater treatment and recycling by bio-flocs technology. The main conclusions were summarized as follows:1. Aim to solve the practical needs of the complex factors and operated conditions of the in-situ BFT system. Based on the response surface method, the quantitative mathematical relationship between key operated parameters and object were obtained, which can be used to simplify the control parameters, as well as the optimization of the operated performance.The statistical approach showed significant results regarding the inorganic nitrogen (TAN) removal performance with operated C/N ratio and flocs sludge concentration. The quantitative mathematical relationship of the response surface model can be described in the form of second-order polynomial equation. The ANOVA results indicated that the model have well validation and fitting. In parameter range, the single factor and their interaction effects shown positive correlation relationship with the response value.The optimum results attained from the model indicated that more than90%TAN removal efficiency was achieved when the C/N ratio was between13-16, as well as the flocs sludge concentration (MLVSS)2.0-2.5g/L. During this circumstance, the effluent quality can be satisfied to the aquaculture water recycling.Based on the interspecific difference of the cultured species, the flocs sludge concentration and C/N ratio can be considered as primary control parameters to ensure the stable and reasonable operation of the in-situ Bio-flocs technology aquaculture system. Under the condition of practice, the parameters value can be appropriate correction based on the consideration of cultured species, stocking density and water quility requriment.2. Base on the problem of in-situ BFT system, such as less applicable objects and limited operated condition, the ex-situ BFT reactor was established for the evaluation of the operated performance using simulated aquaculture wastewater, and the research objectives were focus the operated performance, flocs characteristic and optimization of flocs PHB content. The results indicated that the reactor have well operated performance for the treatment of the simulated aquaculture wastewater. During steady stage, when the influent NH4+-N and COD concentration were28.22±1.83mg/L and627±35mg/L, the corresponding effluent were1.23±1.38mg/L and17±13mg/L, with removal efficiency of95.69±4.92%and97.27±1.89%. The reactor shown stable operated performance during long-time running, and the effluent can be used as aquaculture recycling.The results of the flocs characteristics shown that the stable granulation can be obtained during the steady stage, which means well solid-liquid separation and potential convenience for feed preparation. The flocs ingredient shown well nutritive value, which can be satisfied for the demand of the aquatic animal. The flocs contained43.89%crude protein with reasonable amino-acids ratio, especially in essential amino-acid of threonine, lysine and methionine were1.2836g/100g,3.3965g/100g and1.4699g/100g. The important prebiotics of Vitamin-E and polysaccharide were145.23mg/kg and251.32mg/kg. Accord with the aquatic animal nutritional requirement, the flocs were considered have high feeding value.The typical cycle performance indicated that the alternant anaerobic-aerobic operated mode were beneficial to flocs PHB accumulation. Based on the response surface model batch results, the flocs concentration, C/N ratio and anaerobic time were both have significant effect to flocs PHB yield. The optimized flocs PHB yield of150-200mg/g can be obtained when the parameters in range of:flocs concentration4-7g/L, C/N ratio15-18, and anaerobic time50-85min. Otherwise, with the field PHB application effect analysis, an potential carbon source allocation strategy that based on the FCR (Feed Conversion Rate) was proposed, which in order the balance the carbon substance contention between flocs production and PHB synthesis.3. The pilot-scale ex-situ BFT reactor was established for the evaluation of the anaerobic-aerobic operated performance using actual fish processing wastewater. The research target were for the clarification of the effect with SRT change, which have influence on flocs production and wastewater processing performance, as well as the substance conversion and transportation rule during varied SRT stage (2-15d).During the reactor operated stage (SRT=2-15d), when the influent COD, TN, PO43--P concentration were801.5±201.3mg/L,40.82±12.62mg/L,42.85±14.03mg/L and24.86±5.96mg/L, the according removal efficiency were in range of88.77±1.69%-92.74±1.45%;66.07±3.91%-90.40±2.02%;41.09±2.04%63.20±3.10%and41.81±6.71%-78.27±4.80%.The SRT change was have main effect on transformation path and removal performance of substance N and P rather than COD. Under short SRT condition, the substance removal were main through assimilation, and the N removal performance was better than P. Meanwhile, the nitrification was limited by short SRT, as the effluent NO2--N concentration were4.06±1.15mg/L and9.93±3.11mg/L during SRT2-5d. The nitrification-denitrification performance can be improved by extend SRT, as well as the phosphorus removal performance. The optimal PO43--P removal efficiency was78.27±4.80%during the SRT10d condition.The flocs observed biomass coefficient was influenced by varied SRT stage. During the operated phase (SRT=2-15d), the flocs Yobs value was reduced from0.539±0.092(mg VSS/mg COD) to0.144±0.019(mg VSS/mg COD) with SRT lengthen. Meanwhile, the flocs production performance also decreased from1115gVSS/m3/d to270gVSS/m3/d, as well as the flocs VSS content was reduced from67.31±3.57%to57.92±0.96%. However, the flocs SVI30values have no obvious difference, which indicated that was beneficial to feed material preparation.Overall, due to the relative high substance loading of the fish processing wastewater, the system operation have obvious SRT conflict with N, P removal and flocs production. Consideration of the ex-situ operation characteristic, the wastewater processing performance should be balanced through decreased flocs productive capacity under practical condition, which can be satisfied with aquaculture recycling or emission standard.4. The pilot-scale ex-situ ex-situ BFT reactor was established for the evaluation of the different operated performance using actual fish processing wastewater. The conditions difference were contained different flocs harvest timing and operation mode (A-O-A, A2O2-SBR). The research target were for the integrated system performance of both wastewater treating efficiency and flocs nutrient synergia, which can be achieved by enhanced denitrifying phosphorus removal through rational utilization of the internal carbon source.The reactor operated performance indicated that, when the influent of COD, NH4+-N, TN, PO43--P were479±136mg/L,35.57±9.76mg/L,37.28±9.38mg/L and15.57±5.42mg/L, the according removal efficiency during each stage were in range of90.08±4.62%-92.95±1.72%;85.33±6.82%-90.44±3.17%;69.05±2.61%82.96±4.54%;72.05±2.91%-87.16±4.77%. The effect of different flocs harvest timing and operated mode have no influence on organics removal efficiency obviously. Nevertheless, the nitrogen and phosphorus removal performance was found varied during the foregoing conditions.Based on process characteristic, the TN removal were main through denitrification and denitrifying phosphorus removal, as well as the TP removal depend on aerobic phosphorus removal and denitrifying phosphorus removal. In added consideration of NH4+-N decrease and NO3--N increase, the assimilation have less contribution of TN removal during aerobic-phase at each operated stage.The mass balance results showed that different flocs harvest timing and operated modes have influence of required organics amount for units N, P removal. During the A-O-A operated mode, the different flocs harvest timing lead to the according ratios of COD/P and COD/N were33.92±1.44mg COD/mg TP,19.23±3.4mg COD/mg NO3--N;23.51±3.33mg COD/mg TP,16.78±0.92mg COD/mg NO3--N. During (AO)2-SBR operated mode, the ratios were decreased to19.32±1.53mg COD/mg TP and14.28±0.50mg COD/mg NO3--N.Based on inner carbon source utilization balance, the PHB consumed mass percentage on aerobic and anoxic phase at each stage were73.21±2.73%,24.53±1.36%;77.76±1.44%,24.72±4.52%;63.06±9.94%,35.60±9.16%. The PHB consumed ratio was improved in anoxic phase during (AO)2-SBR operated mode, which can be provided material basis for the enhanced denitrifying phosphorus removal performance. The N, P removal stoichiometric relationship at anoxic phase was increased from1.75±0.23mg TP/mg NO3--N to2.13v1.03mg TP/mg NO3--N during each stage. According to the results of batch experiments, the denitrifying polyphosphate-accumulating organisms (DNPAOs) in polyphosphate-accumulating organisms (PAOs) ratios were increased from11.90%to45.14±2.24%.Overall, for the integrated operated purpose of wastewater treating efficiency, particularly in the practical needs of flocs PHB synthesis and harvest during the productive period concurrently, the improved denitrifying phosphorus removal performance can be used as core control strategy for system stable operation and recycling, which can be achieved by efficient utilization of internal carbon source.5. The ex-situ BFT reactor was established for the evaluation of the operated performance using quasi-full scale recirculation aquaculture system. The system performance were compared when the cheap internal carbon source were supplied at aerobic-or anoxic-phase or no added under the A-O-A operated mode. The research targets were main improved the sustainability of the RAS system, which can be achieved by using the potential carbon source of the system itself, as well as for the wastewater treatment and recycling by bio-floes technology.The reactor operated performance indicated that, when the influent COD, NH4+-N and PO43--P concentrations were444±98mg/L,43.22±8.90mg/L and17.67±3.92mg/L, the according removal performance were86.87±2.89%-90.49±1.02%,74.19±4.39%-89.26±4.74%and76.49±1.60%-89.45±3.00%.The optimal treating performance can be achieved by the added carbon source supplied to aerobic-phase, when the influent NH4+-N and PO43--P concentrations were41.59±6.49mg/L and17.08±2.05mg/L, the according effluent concentrations were4.69±1.32mg/L and1.78±0.48mg/L, with high removal efficiency of88.33±3.91%and89.45±3.00%, and can be used for the aquaculture reuse.Based situation of the inner carbon source utilization, the PHAs consumed rate at aerobic time of the phase Ⅱ were2.70±0.21mg PHAs/g VSS/h, which lower than the3.26±0.22mg PHAs/g VSS/h (Phase Ⅰ) and4.04±1.07mg PHAs/g VSS/h (Phase Ⅲ), as well as the anoxic time PHAs consumed rate of1.88±0.20mg PHAs/g VSS/h, which higher than the1.52±0.42mg PHAs/g VSS/h (Phase Ⅰ) and1.02±0.23mg PHAs/g VSS/h (Phase Ⅲ), these implied that the phase Ⅱ might have more abundant PHAs at anoxic time, which can be improved the denitrifying phosphorus removal performance. Base on the batch experiments, the DNPAOs in the PAOs ratios that concluded by the phosphorus rate were27.62±4.14%,46.45±5.38%and24.90±2.16%.Based on the microorganisms yield model, when the substance flow of COD and TN were6.98±0.87g COD/d,0.97±0.11g TN/d;7.28±0.23g COD/d,1.13±0.10g TN/d;8.50±0.37g COD/d,1.13±0.01g TN/d, the conversion rate of C and N were44.92%,25.36%;54.59%,24.89%;50.89%,27.04%during each stage. In addition, according with the high heterotrophic bacteria ratio and low nitrifying bacteria ratio, as well as the enhanced denitrifying phosphorus removal performance, the phase Ⅱ were considered achieved a reasonable substance utilization approach, which meet the dual purpose for wastewater treatment and flocs production.Overall, consider of the wastewater characteristic with high NO3--N concentration in RAS effluent, the supply fish feces as organic carbon can obvisously increase the system performance and substance utilization rate, and the aerobic phase fesces supply strategy have the best flocs yield and effluents quility, which can be used as technical base for the realization of engineering applications. |
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