Utilization And Nutrients Recovery Of Anaerobic Digestion Effluent After Membrane Treatment Based On Microalgae For Energy Production

With the development of economic and living stardand of China,the conmpustion of eggs and meat increased a lot.Due to the increasing of labor cost and high efficiency demand,the intensive and large-scale poultry-raising industry developed fast in China.Along with the poultry-raising industry,poultry waste and wastewater are becoming a new chanllege affecting the livelihood.Positively respond to the call of hormounious development of animal husbandry by the Chinese government,anaerobic digestion is applied to the poultry manure to produce biogas and biofertilizer.Meanwhile,a kind of high ammonia contained wastewater was produced during the production of biofertilizer.This study combined wastewater treatment and microalgae cultivation,using microalgae as the carrier to realise nutrients recovery and bioenergy production.The characteristics of wastewater was studied,and certain methods(dilution/air stipping/electrolysis)were used to pretreat the wastewater for microalgae cultivation.After pretreatment,the wastewater with NH4+ concentration of 20 mg/L and 250 mg/L was used to cultivate S.platensis and Chlorella sp.,respectively.The removal of NH4+ has a positive relationship with the air stripping time.A higher temperature could enhance air stripping.Results showed the longer the electrolysis process time was,the higher the removal ratios of NH4+,total organic carbon(TOC)and inorganic carbon(IC)were.The highest removal efficiencies of NH4+,TOC and IC in electrolysis were 47%,76%and 96%,respectively.The removal efficiency of NH4+ was 10-65%during microalgae cultivation.The NH4+concentration after microalgae treatment could meet the discharge standard of pollutants for livestock and poultry breeding in China.In all,dilution would be the optimal solution for pretreatment to wastewater.A two-stage system was built up to harvest microalgae and recycle culture medium.Different methods were applied to harvest microalgae,including UF and centrifugation.When the microalgae were in the steady growth phase in the first stage,the UF or centrifuge was applied to harvest microalgae and recycle culture medium.Then the recycled culture medium was used to cultivate S.platensis.The results showed the two-stage cultivation system produced high microalgae biomass including 0.39 g/L Chlorella sp.and 3.45 g/L S.platensis in the first-stage and second-stage,respectively.In addition,the removal efficiencies of NH4+ reached 19%and almost 100%in the first and the second stage,respectively.Total phosphorus(TP)removal reached 17%and 83%,and total organic carbon(TOC)removal reached 55%and 72%in the first and the second stage,respectively.This study provides a new method for the combined of pure microalgae cultivation and wastewater treatment with culture medium recycling.By using the harvest system mentioned in previous chapter,the whole system can save 28 Yuan/kg microalgae.In this chapter,CO2 was used as carbon supply to enhance microalgae production.CO2 ranged from 0.038%to 99%were supplied for Chlorella.The results showed 1%CO2 would fit the requirement of microalgae in lab-scale culture(working volume of 200 mL).When CO2 concentration is too high,there would be negative of CO2 to the microalgae.The concentrations of chlorophyll a and b from the 10%CO2 run is the highest.The temperature has an effect on the growth of microalgae:microalgae was inhibited at 20℃ grew well at 25℃ and 30℃,and had the highest growth rate at 35℃.The components of microalgae have a significant effect on the utilization on the microalgae.There are several factors(environment,salinity of culture medium,reactor type)that contribute to the different components of microalgae.Among which,the reactor type and the content of culture medium showed the great influence on the composite of microalgae.In this chapter,poultry wastewater was used to cultivate Chlorella sp.in bench-scale ponds,and BG11 culture medium was set as control.The impact of open system and closed system on ash content of microalgae was investigated.The ion contents of microalgae and algal ash were tested to reveal the component of the ash.Results showed that ash content,lipid content and protein content of microalgae cultivated in closed system were respectively about 3%,5%and 10%lower compared with that of microalgae cultivated in the open system.Results showed that microalgae cultivated in wastewater with higher salinity resulted in higher ash content,low lipid and low carbohydrate,and the ash content of microalgae in 3.59 g/L salinity wastewater was 12.5%higher than that in 1.50 g/L salinity wastewater.This research aims to put forward a way to reduce the ash content of microalgae when coupling microalgae cultivation with the wastewater treatment.By scale-up the cultivation of microalgae,PBR and raceway pond were compared from the aspect of the efficiency of culture and cost.The PBR can remove 40%of the NH4+ and 75%of TP in the culture medium.The microalgae can produce 135 mL methane/VS g microalgae by experiment or produce 33%bio-crude oil based on calculation.