| The impact of aquaculture on the environment has received more and more attention in recent years,especially the freshwater pond aquaculture,which still has some problems such as backward facilities,equipment and poor controllability,has a great impact on the environment.As an emerging aquaculture model,the in-pond raceway system(IPRS)has achieved rapid development.However,the current research is still lacking in the adaptability of different cultured species to IPRS and the performance evaluation of this model.Solids removal process is also single and receives relatively little attention;in addition,improving the automation of supporting equipment during the development trend of standardization,scale and technology integration of this model is still needed.In view of the above-mentioned circumstances,from the perspective of practical production,the water quality characteristics and benefit analysis of an improved IPRS,the study of the particle size distribution(PSD)of suspended solids in the raceways water,and the design of the multi-mode control system of multiple rotating microscreen drum filters and the optimization of the transmission system were carried out.Relevant research can provide reference for the further improvement and optimization of IPRS,and more targeted selection of water treatment methods and improvement of system equipment automation.The main research contents and conclusions are as follows:1.By improving the existing IPRS,the drum filters and the automatic suction equipment are used together to remove the solids generated during the culture process.Based on this,the system water quality and benefit were analyzed.The system mainly raised hybrid snakehead(Channa argus?× Channa maculata ?),black carp(Mylopharyngodon piceus)and Megalobrama terminalis(?)× Culter alburnus Basilewsky(?)hybrids,co-cultured silver carp(Hypophthalmichthys molitrix),bighead carp(Aristichthys nobilis),crucian carp(Carassius auratus)and freshwater shrimp.A technique consisting of installing drum filters and automatic suction equipment,planting aquatic plants,and culturing filter-feeding and omnivorous animals was adopted in situ remediating the culture water bodies.Ex situ remediation of the wastewater bodies by the combination of constructing sedimentation basins and the purification pond was also investigated.The results showed that comprehensive regulation and control of water quality was an effective means to improve water quality.During the test,the ranges of water temperature,dissolved oxygen(DO),pH,total ammonia nitrogen(TAN)and nitrite nitrogen in the raceways were 9.09 ± 0.01?25.51 ± 0.03?,5.64 ± 0.23?11.78±0.54mglL,6.55±0.13?8.42 ±0.14,0.58±0.06?1.79±0.05mg/L and 0.09±0.00-0.61±0.02mg/L,respectively,which were all within the reference range.The purification pond has a significant improvement on the wastewater quality,the average removal rates of TAN and nitrite nitrogen from the sedimentation basins were 58.85%and 60.36%,respectively.The output value and benefit analysis(return on investment:35.69%.benefit cost ratio:1.36)indicated that IPRS has obtained better aquatic product yield and economic benefits.Overall,IPRS can achieve better comprehensive benefits.2.The PSDs of suspended solids in the IPRS raceways were measured by laser method.Based on this,the PSDs characteristics of the solids were analyzed,and the PSDs models were established.The results showed that relatively stable PSDs was observed throughout the experiment.For the number distribution,50%of the particles'size was approximately smaller than 2.70 ?m,98%of the particles' size was approximately smaller than 2 ?m,whereas for the volume distribution,50%of the particles' size was approximately less than 20.00 ?m,98%of the particles' size were approximately less than 140.00 ?m.Judging from both,about 80%of small particles(<5.04 ?m)by number contributed about 10%to the total particle volume,while about 20%of particles(? 5.04 ?m)by number contributed about 90%to the total particle volume.It can be concluded that although the number of small particles was large,its contribution to the volumetric distribution was small,whereas the number of big particles was small,its contribution to the volumetric distribution was large.PSDs models showed that both power-law model(R2 ? 0.899±0.033)and the variable-?model(R2 = 0.975±0.011)fitted the number distribution very well,but the latter was better;the log-normal distribution model(r2 ? 0.968±0.020)fitted the volume distribution well,PSDs characteristics and models analysis can provide reference for understanding the evenness of PSDs and the choice of water treatment methods.3.Design and experiment of multi-mode control system of multiple rotating microscreen drum filters based on programmable logic controller(PLC)and the optimization of transmission system of the drum filter were carried out.The results showed that the operation control of ten drum filters in manual,automatic and timing modes were realized.In the manual mode,the reducer and the backwashing pump can be controlled to start and stop at any time according to requirements;in the automatic mode,one low level and one high level switch were used to jointly control the start and stop of the reducer and the backwashing pump,when the low and high level switches were triggered by the water in the drum,the backwashing performed,when the water level was lower than the low level switch,the backwash stopped,and when the water level failed,a high level was trigged outside the drum and the system didn't conduct backwash;in the timing mode,the backwashing time and interval time can be set according to the water quality,this mode will be very practicable and economical when the level switch encounter a problem.This kind of control method can not only save costs,but also improve the automation level of the drum filter.In addition,the improved cycloid reducer(0.12kW)and the bevel gear drive have the advantages of low energy consumption and smooth transmission compared to the original worm gear reducer(0.18kW)and chain drive. |
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