| Phosphorus is an indispensable element of fish. But the utilization of phosphorusin diets is lower, and most of it discharged into the water as phosphate causedphosphate accumulation. Also long-closed running recirculating aquaculturesystem(RAS) resulted in the accumulation of nitrate. High concentration of phosphateand nitrate in RAS wastewater often affect the normal growth and development andalso can cause eutrophication when let it into the lake and river.Anaerobic/anoxic/aerobic(A2/O) process of activated sludge is widely used tonitrogen and phosphorus removal especially in sewage runoff, industrial waste and soon. But there were hardly any studies of nitrogen and phosphorus removal in RASwastewater. This experiment used the A2/O process studied the nutrient removal of theRAS wastewater from the following parts:Part1:The effect of nitrate concentration in anaerobic segment to A2/O processnitrogen and phosphorus removal.Research on nitrogen and phosphorus removal efficiency in the stable operationof the A2/O-SBR nitrogen and phosphorus removal reactor, artificial waterdistribution as a treatment target, increase the anaerobic influent nitrate concentrationgradient in turn. The results showed that:(1) PO43--P、TP removal in NO3--N≤50mg/L in the anaerobic water removal rate is better, were95.33±5.35%、92.12±5.07%；In the case of NO3--N≥50mg/L, with the removal of NO3--N concentration increasedwas significantly decreased, which PO43--P removal and removal and water NO3--Nconcentration was linearly correlated, the regression equation wasY=-1.2648X+151.43〔X---NO3--N (mg/L); Y---PO43--P removal; R2=0.9981〕;When the influent NO3--N≥90mg/L, the effluent TN concentrations greater thanwater.（2）NO3--N、TN removal rate highest in30≤NO3--N≤70mg/L, were70.94±6.14%、80.85±3.67%.（3）The effect of NH4+-N、NO2--N removal is less by NO3--N concentration, can mainain a high removal rate, were94.75±4.35%、86.54±8.65%.Part2: The effect of ammonia concentration in anaerobic segment to A2/Oprocess nitrogen and phosphorus removal.Research on nitrogen and phosphorus removal efficiency in the stable operationof the A2/O-SBR nitrogen and phosphorus removal reactor, artificial waterdistribution as a treatment target, increase the anaerobic influent ammoniaconcentration gradient as2,4,6,8mg/L in triplicate in turn. The results showed that:(1) The removal effeciency of total phosphorus and phosphate had a significantchanges with the influent ammonia concentration. The TP and phosphate removal inNH4+-N≤6mg/L was low and by a liner increase as the influent ammoniaconcentration increased. When the NH4+-N≥6mg/L, the TP and phosphate had asteadily removal rate, the average removal rates were95.36±0.90%,94.33±2.22%respectively.(2)The influent ammonia concentration affected the removal rate of totalnitrogen, nitrate showed a slight downward rend as the influent ammoniaconcentration increased. The average removal rate of total nitrogen and nitrate was95.36±0.90%,94.33±2.22%respectively throughout the process.(3)The ammonia andnitrite had a smaller effect with the influent ammonia concentration, the averageremoval rates were69.24±3.68%,71.12±4.07%respectively in the A2/O process.Part3: The Effect of COD/P on the RAS Wastewater Treatment in A2/O ProcessThis part is amied to introduce our study on using the anaerobic/anoxic/aerobicprocess in sequencing bath reactor (SBR-A2/O) to treat recirculating aquaculturewastewater under different COD/P ratios. Wastewater from recirculating aquaculturesystem (RAS) is likely to accumulate nitrate and phosphate. In this study the RASwastewater was high in total nitrogen, nitrate nitrogen, and phosphate concentrations,which were50~70mg/L,50~80mg/L, and9.4~10.7mg/L, respectively. And ourexperiments indicate that the removal efficiencies of total nitrogen and totalphosphorus were low when the COD/P ratio was lower than19.85and increasedsignificantly with the increase of COD/P ratio. When the COD/P ratio was greaterthan19.85, the removal efficiencies of total nitrogen and total phosphorus keep stableand the average removal rate were62.38±8.33%and62.44±4.97%in the treatment ofrecirculating aquaculture wastewater by SBR-A2/O process, respectively. The COD/Pratio was range from25to30in water at the last period of the experiment and theremoval of total nitrogen, total phosphorus, nitrate, phosphate, ammonia, and nitrite were relatively stable with an average removal efficiencies of60.61%,62.69%,60.21%,60.46%,45.55%, and84.94%, respectively. The high ammonia concentrationin influent had a great effect on SBR-A2/O process. With an ammonia concentrationof16.07±1.09mg/L and COD/P ratio less than22.49mg/L in the wastewater of RAS,the SBR-A2/O process was greatly impacted and the effluent nitrite concentration wassignificantly higher than that in the influent.nitrite concentration. The highestaccumulation of nitrite was up to6.79±3.39mg/L with influent COD/P ratio of17.21.However, the nitrite could be100%removed when the ratio of COD/P was above22.49. The experimental results also have shown that ammonia removal efficiencywas not affected by COD/P ratio and the average removal efficiency was87.29%intreating wastewater of RAS by SBR-A2/O process.Part4: Recerch on the effect of nitrogen and phosphorus removal when PCL ascarbon in process of anaerobicThe study aquaculture wastewater nitrogen and phosphorus removal, depend onlong-running RAS aquaculture wastewater, using A2/O process, and PCL as anaerobiccarbon source. The results showed that:(1) PCL applied to the A2/O process activatedsludge wastewater treatment farming, arly as anaerobic required carbon, nitrogen andphosphorus to achieve better results, TP、PO43--P average removal were93.82±5.75%、86.85±9.13%; TN、NO3--N removal reactor operation with a downward trend, TNremoval rate from85.30%down to28.24%, NO3--N removal rate from78.63%downto28.04%;(2) PCL is wrapped in a late-stage trial of activated sludge floc formation,unable to supply anaerobic denitrifying bacteria phosphorus carbon source, so thatnitrogen and phosphorus removal rate dropped significantly.(3) NH4+-N and NO2--Nremoval rate changed little, remaining high removal rate, the average removal ratereached69.97±23.26%,87.29±28.81%. Overall in the PCL as the carbon sourceused in A2/O process aquaculture wastewater, May well be used by PAO or anaerobicdenitrifying bacteria in paragraph phosphorus. Because of its late will be wrapped,can not continue to release carbon, resulting in lower rates of nitrogen and phosphorusremoval, so place it in the form and cleaning and replacement interval period of timestill need further study. |
PDF Full Text Request