Pretreatment Method Of High Ammonia Concentration Piggery Biogas Slurry For Green Algae Culturing

With the rapid development of livestock and poultry industry, there are largeamounts of swine manure wastewater produced each day all over the world, whichcause serious environment issue if discharged improperly. Nowdays, anaerobicfermentation is the mostly common method for reducing the organic substance ofswine wastewater, while anaerobic fermentation slurry still has high value ofnitrogen and phosphorus content, for example, the ammonia nitrogen content can be600-2000mg/L. Microalgae-based pig slurry treatment attracts more and moreattention due to unique advantages of low cost, simple operation and smallecological footprintand the fact that they could effectively utilize slurry of organicmatters e.g., e N, P and other nutrients. Scenedesmus obliquus, as an idealpollution indicator due to their high tolerance to the environment, was used forwastewater treatment by many researchers. In this paper, Scenedesmus obliquus wasused for the piggery biogas slurry purification especially for ammonia removal. Inaddition, the effect of co-culture of Scenedesmus obliquus and Chlorella for biogasslurry treatment was systematically examined. The main results are as follows:Scenedesmus obliquus was inoculated into the anaerobic fermentation biogasslurry with different dilutions respectively to study their effect on pig biogas slurrypurification and oil accumulation. The results showed that, Scenedesmusobliquus could grow well at different dilution of10%,30%and50%ofpiggery biogas slurry with efficient nutrient removal in10days cultivation. In the10%dilution solution, Scenedesmus obliquus showed fast growth and the removalefficiency of the TN, TP and ammonia nitrogen were43.55%、38.39%and55.29%respectively. Scenedesmus obliquus had a cumulative effect on oil in biogas slurry;the highest oil content of22%was reached when grown in50%piggery biogasslurry. And the oil content of19%was obtained in10%dilutions biogas slurry. Acouple of methods were adopted in order to remove the ammonia efficiently. Theresults showed that, when introducing the nitrifying bacteria into the biogasslurry, the growth and ammonia nitrogen removal was not obvious compared with the control. Struvite crystallization process was affected by other factors and theeffect of adding phosphate, magnesium and regulating pH value on the degradationof ammonia is minimal; zeolite had limited adsorption effect for ammonianitrogen, and the adsorption capacity of ammonia nitrogen for artificial zeolitewithout the activation after anaerobic fermentation of pig slurry was3.05mg/g.When zeolite was used in biogas slurry for ammonia activation andadsorption, the results showed that adsorption ability of the ammonia nitrogen underthe condition of aeration and standing conditions after14h was37.08%. In theexperiment of different treatment including salt treatment, heat treatment, acidtreatment and ferric chloride treatment for zeolite activation, the results showed thatsalt treatment was the best among all treatment and the adsorption capacity was4.56mg/g, followed by unactivated zeolite. And the adsorption capacity was highestwith salt solution at a concentration of0.5mol/L. It is worth noting that for zeolite,the ammonia adsorption capacity was about5mg/g at the first cycle, and thengradually decreased, after25cycle’s adsorption-desorption process, the value of theadsorption capacity come down to about3mg/g at room temperature.Through the experiment of growing Scenedesmus obliquus on piggery biogasslurry after zeolite adsorption, it showed that after24h, all the indexes of waterquality declined and total nitrogen、total phosphorus、ammonia nitrogen and CODvalues reduced31.71%,62.23%,53.59%and22.44%, respectively. WhileScenedesmus obliquus can not survive when inoculated into slurry withoutpretreatment. The OD680at the end of the experiment was0.997and water qualityindexes were declined, which showed that the water quality decreased rapidly sincethe second day and basically tended to be stable at ninth day. The indexes of waterquality for total nitrogen、total phosphorus、ammonia nitrogen and COD valuesreduced as99.13mg/L、43.61mg/L、2.05mg/L and200.52mg/L respectively.Scenedesmus obliquus accumulated30%oil content in biogas slurry without dilution,which had better oil accumulation compared to Scenedesmus obliquus in chaptertwo.Research on Scenedesmus obliquus and Chlorella jointly dealt with pig slurryshowed that both Chlorella and Scenedesmus obliquus could grow well in the biogas slurry after pretreated by zeolite, and Chlorella showed more tolerant thanScenedesmus obliquus in the slurry. In the co-culture experiment, it showed thatChlorella had stronger competitiveness and ability to inhibit the growth of otherorganisms, and when Scenedesmus obliquus and Chlorella inoculation ratio was1:3, Chlorella obtained maximum biomass and maximum growth rate among theco-culture experiments which inoculated with15×104cells/mL at first and increasedas174×104cells/mL at the end of experiment; when chlorella cultured alone hadthe best purifying effect on the slurry of treatment groups, followed by1:3co-culture system microalgae. All experimental groups show purifying effect onwater quality.