Algae-algae Co-culture To Purify Cattle-ranch Wastewater Coupled With Bio-fertilizer And Its Growth-promoting Effects On Wheat

Agricultural non-point source pollution caused by livestock wastewater severely restricts the healthy and sustainable development of agriculture and the improvement of the ecological environment of human settlements.Traditional livestock wastewater treatment had some disadvantages such as high costs,low nutrient removal,poor purification effects,and easy to produce secondary pollution.Microalgae,some kinds of unicellular photoautotrophic organisms,have a variety of culture models such as autotrophic,heterotrophic and mixtrophic,and some microalgae can grow in livestock wastewater.The screen of specific algae strains that can grow rapidly in specific livestock wastewater,and the establishment of the corresponding wastewater treatment system based on microalgae culture are the key factors for the treatment of livestock wastewater and resource recovery in this way.In this paper,cattle farm wastewater was used as the experimental livestock wastewater source,in order to select the algae strains that can grow effectively in the wastewater and have high biomass yield,the tolerance and growth characteristics of 7 different microalgae strains were tested.Secondly,the cultivation condition was optimized and the effect of wastewater purification was determined.The algae-algae co-culture system was constructed based on the selected target algae strains,and the removal rate of nutrients in wastewater and microalgae biomass yield were also studied.Lastly,the effects of bio-fertilizer based on microalgae biomass on wheat seed germination,seedling growth and soil nutrients were explored.The main findings are as follows:1、Combine C.vulgaris,C.pyrenoidosa,S.quadricauda,C.emersonii,S.obliquus,Spirulina and Chlorella sp.DT01 isolated from power plant wastewater were respectively cultured in origin cattle farm wastewater and different diluted wastewater to test the adaptability and growth characteristics of different microalgae strains.The results showed that algal strains Chlorella sp.DT01,C.pyrenoidosa and C.vulgaris exhibited strong tolerance and good growth in wastewater.The highest biomass content in origin wastewater was Chlorella sp.DT01(1.07 g/L).The highest biomass contents in 2,4,and 6-fold diluted wastewater were Chlorella sp.DT01(0.83 g/L),C.vulgaris(0.99 g/L)and C.pyrenoidosa(0.94 g/L)respectively.Therefore,these three microalgae strains were selected for follow-up experiments.2、The three selected excellent algae strains were respectively cultured into the origin cattle farm and different diluted wastewater to detect the removal rate of ammonia nitrogen,total phosphorus and COD in the wastewater.The results showed that the growth of the three algae strains was significantly related to the dilution rate.Among them,C.pyrenoidosa had strong tolerance to origin wastewater,and grew better than BG11 in the original solution.The biomass content was 2.70 g/L,and the removal rates of ammonia nitrogen,total phosphorus and COD are 96.12 %,48.72 % and 3.17 % respectively.The Chlorella sp.DT01 is also tolerant to origin wastewater and grew better than BG11.Its dry weight of microalgae is as high as 2.60 g/L,and the removal rates of ammonia nitrogen,total phosphorus and COD are 94.65 %,48.08 % and 5.92 % respectively.However,C.vulgaris had poor tolerance to wastewater and couldnot grow in the original solution.The dry weight in the 4-fold dilution was only 1.65 g/L,which was significantly lower than BG11.The removal rate of ammonia nitrogen,total phosphorus and COD was96.83 %,65.79 % and 1.90 % respectively.The results once again proved that C.pyrenoidosa and Chlorella sp.DT01 were excellent algae strains for treating the raw liquid of cattle farm wastewater.3、The algae-algae co-culture system was constructed based on Chlorella sp.DT01 and C.pyrenoidosa strains with different ratios.The results indicated that the highest dry weight of the microalgae reached 2.80g/L after 1:1 combination of the two types of microalgae cultured in raw wastewater for 14 days,which was significantly higher than the biomass obtained by culturing single algal strain.Similar,the combined culture had significantly higher levels of nutrient removal in the original wastewater solution,and the removal rates of ammonia nitrogen,total phosphorus and COD reached 96.70 %,72.45 % and 30.55 %,respectively.Obviously,this algae-algae co-culture system can effectively remove nutrients and COD in wastewater,and at the same time obtain high amounts of microalgae biomass.4、Biomass obtained by culturing microalgae using wastewater were used as bio-fertilizer and the wheat seed germination,seedling growth,dry matter accumulation and soil nutrients were tested.The results showed that the microalgae bio-fertilizer can significantly promote the growth of seedlings.The height,fresh weight and dry weight of wheat seedlings in microalgal bio-fertilizer adding treatments were increased by 48.08 %,155.79 % and 124.14 %,respectively,compared with the control.Application of microalgae bio-fertilizer could also improve the photosynthesis and root vitality of seedlings.In addition,the microalgae bio-fertilizer could also increase the nitrogen,phosphorus and potassium content in the soil,and significantly improved soil nutrients.In summary,two excellent algae strains that can grow effectively in cattle farm wastewater were screened.The algae-algae co-culture system based on the two algal strains with 1:1 mix rate could effectively remove nutrients and COD in wastewater,and obtained high amounts of microalgae biomass and better purification effect.In addition,microalgae biological fertilizer could significantly improve soil nutrients and promote the healthy growth of wheat seedlings,which could be used as a new type of biological fertilizer for agricultural plant production.The findings of this study provided a scientific basis for constructing an novel algae-algae system to purify livestock wastewater and produce fertilizers.