Mariculture Wastewater Treatment With Microalgae And Process Enhancement

With the increasing demand for aquatic products and the exhaustion of traditional aquatic resources,mariculture industry has developed fast,accompanying the generation of large volumes of aquaculture wastewater.Using microalgae to purify mariculture wastewater not only can enhance water quality and reduce environmental risks after wastewater discharge,but the generated microalgae biomass can also be used for feed and other extended industries to obtain higher economic benefits.However,there are still some shortcomings such as slow growth of marine microalgae suitable for wastewater treatment,low nitrogen and phosphorus removal efficiency,and no mature treatment system.In order to solve the above problems,several investigations were carried out as below:Firstly,screening of advantageous algal strain for mariculture wastewater treatment was carried out.The results showed that after 7 days of culture,the dry weight of marine Chlorella sp.was 0.63 g/L,the maximum specific growth rate was 0.50 d^-1,the removal rate of total nitrogen（TN）was 66.4%,and the removal rate of total phosphorus（TP）was 94.30%.The removal rates of TN and TP were 101～253%and 9～53%higher than those of other algae species.Marine Chlorella sp.showed the best growth characteristics and nitrogen and phosphorus removal ability in mariculture wastewater.Considering the growth and nitrogen and phosphorus removal capacity of marine Chlorella sp.,0.2 g/L was determined to be the best inoculation concentration of this strain for mariculture wastewater treatment.The performance of Marine Chlorella sp.in treating mariculture wastewater with various strengths was investigated.The results showed that the removal rates of TP in low,medium and high strength wastewater by marine Chlorella sp.were91%,94%and 85%,respectively,and the removal rates of TN were 41%,68%and 49%,respectively.After microalgal treatment,the nitrogen and phosphorus concentrations in low strength wastewater met the discharge standard（SC/T 9103-2007）and reuse standard（GB18918-2002）.In order to further improve the performance of microalgal mariculture wastewater treatment,pre-starved marine Chlorella sp.was used to retreat the mariculture wastewater with different concentrations of nitrogen and phosphorus.The results showed that the removal rates of TP from low,medium and high strength wastewater by pre-starved marine Chlorella sp.were 100%,100%and 93%,respectively,and the removal rates of TN were 82%,69%and51%,respectively.After the above treatment,the nitrogen and phosphorus concentrations of low and medium strength wastewater met mariculture wastewater discharge and wastewater reuse standards.A two-stage microalgae mariculture wastewater treatment system was established to further improve wastewater purification performance.The results showed that when the hydraulic retention time was 1 day and after 7 cycles of treatment,the two-stage system could treat the high strength wastewater to satisfying the discharge and reuse standards.To sum up,this study screened a strain of marine Chlorella sp.suitable for the purification of mariculture wastewater,and explored the optimal inoculation concentration of this strain in mariculture wastewater.Meanwhile,nitrogen and phosphorus removal were studied for three strengths of mariculture wastewater.Starvation pretreatment improved the nitrogen and phosphorus removal ability of microalgae within a short period of time,which made the low and medium strengths mariculture wastewater meet the discharge and reuse standards after treatment.A two-stage microalgal mariculture wastewater treatment system was established,and high strength wastewater after treatment by this system could meet the discharge and reuse standards.