Study On Nutrients Recovery From Piggery Wastewater And Starch Wastewater From Bread-making Plant Via Algae-bacteria Symbiotic System

Piggery wastewater contains a large amount of nitrogen,phosphorus and organic matter.Starch wastewater mainly contains starch and protein.If piggery wastewater and starch wastewater were discharged directly without treatment,they would lead to waste of resources and inevitably cause great pollution to the surrounding environment.With appropriate methods,a large amount of nitrogen,phosphorus,starch,and protein contained in piggery wastewater and starch wastewater can be recovered.At the same time wastewaters were treated.To recover the nutrients from starch-piggery mixed wastewater,nutrients recovery technology was developed.This is important for resource recovery and environmental protection.Macromolecular organic matter such as starch and protein in starch wastewater can not be utilized directly by Chlorella vulgaris.The acid conditions were not conductive to the cell growth of Rhodobacter sphaeroides.In this study,piggery wastewater and starch wastewater were used as raw materials.Chlorella vulgaris and Rhodobacter sphaeroides were used as algae and bacteria to construct a symbiotic system of bacteria and algae.A symbiotic system of bacteria and algae was established.Nutrients of starch-piggery mixed wastewaters were recovered by the symbiotic system of bacteria-algae.Starch-piggery mixed wastewaters were purified.The nutrients recovery efficiencies of starch-piggery mixed wastewaters were improve.The processing costs were significantly reduced.In this study,the physicochemical properties of starch wastewater and piggery wastewater were firstly characterized.On this basis,a technology for nutrients recovery of starch-piggery mixed wastewaters was established by the symbiotic system of bacteria and algae.Nutrients recovery effect was characterized.Cell composition of the recovered Chlorella vulgaris and Rhodobacter sphaeroides was characterized.The above work laid a foundation for industrial application.The main research contents and conclusions are as follows:The physicochemical properties of starch wastewater and piggery wastewater were characterized,respectively.The results showed that p H values of starch wastewater and piggery wastewater were 3.6 and 6.7,respectively.Two wastewaters were rich in carbon,nitrogen,phosphorus and other substances.The concentrations of ammonia nitrogen,total phosphorus,total nitrogen,inorganic carbon,total carbon,and chemical oxygen demand were 878 mg L^-1 and 385 mg L^-1,154 mg L^-1 and 55 mg L^-1,1492 mg L^-1 and 496 mg L^-1,3450 mg L^-1 and 337 mg L^-1,36830 mg L^-1 and 520 mg L^-1,58560 mg L^-1 and 1020 mg L^-1.The results showed that the carbon-nitrogen ratio（C:N）of piggery wastewater was 1:1,and the low C:N was not conducive to cell growth of Chlorella vulgaris and Rhodobacter sphaeroides,respectively.While the C:N of starch wastewater was 25:1,and too high C:N was not conducive to cell growth of Chlorella vulgaris and Rhodobacter sphaeroides,respectively.The mixture of piggery wastewater and starch wastewater could balance the C:N,which was beneficial to cell growth of Chlorella vulgaris and Rhodobacter sphaeroides.Elemental analysis found that the concentration of K(36.0 mg L^-1)in starch wastewater was the highest.Starch wastewater also contained Mg,Ca,Fe,etc.The piggery wastewater had the highest Ca concentration of 36.8 mg L^-1.It also contained K,Mg,Fe,etc.Cu only existed in piggery wastewater.Cr,As,Se,Cd and Pb were not found in either wastewater.K,Ca,Mg and Fe contained in starch wastewater and piggery wastewater are necessary elements for cell growth of photosynthetic microorganisms.Therefore,starch wastewater and piggery wastewater were good natural media for Chlorella vulgaris and Rhodobacter sphaeroides.An experiment of nutrients recovery from starch-piggery mixed wastewaters by the symbiotic system of bacteria-algae was carried out.The results showed that both Chlorella vulgaris and Rhodobacter sphaeroides could survive in piggery wastewater.Rhodobacter sphaeroides can survive in starch wastewater.But Chlorella vulgaris can not survive in starch wastewater.This indicated that Rhodobacter sphaeroides could use starch to grow,while Chlorella vulgaris can not use starch to grow.However,the recovery efficiency of wastewaters by Chlorella vulgaris or Rhodobacter sphaeroides was low.The recovery efficiencies of ammonia nitrogen,total nitrogen,total phosphorus and chemical oxygen demand by Chlorella vulgaris in piggery wastewater were 36%,30%,43%and 41%.The recovery efficiencies of ammonia nitrogen,total nitrogen,total phosphorus and chemical oxygen demand by Rhodobacter sphaeroides in piggery wastewater were 37%,35%,33%and 32%.The recovery efficiencies ammonia nitrogen,total nitrogen,total phosphorus and chemical oxygen demand by Rhodobacter sphaeroides in starch wastewater were 41%,38%,37%and 35%.The efficiencies of nutrients recovery from starch-piggery mixed wastewater by the symbiotic system of bacteria and algae were significantly enhanced.Chlorella vulgaris and Rhodobacter sphaeroides formed a symbiotic system.On the one hand,Rhodobacter sphaeroides degraded starch into monosaccharides that can be used by Chlorella vulgaris.On the other hand,the metabolized product of Chlorella vulgaris was alkaline,which ensured the weak alkaline environment required for cell growth of Rhodobacter sphaeroides.It formed a mutually beneficial symbiotic relation.The recovery efficiencies of bacteria and algae symbiosis system for starch-piggery mixed wastewater were more than 95%.It was feasible to recover nutrients from starch-piggery mixed wastewaters rich in nitrogen and organic carbon.After resource recovery,the chemical oxygen demand（COD）,ammonia nitrogen（NH₄⁺-N）and total phosphorus（TP）concentrations of starch-piggery mixed wastewaters were 320 mg L^-1,0 mg L^-1 and 3 mg L^-1,respectively,which met the discharge standards of livestock and poultry wastewater in China.After nutrients recovery,the Algae-bacteria biomass was obtained.The biochemical composition characterization showed that the biomass mainly contained three biological macromolecules,protein,lipid and carbohydrate.The three biological macromolecules accounted for more than 84%of the dry weight of cells.Protein content（59%+）was the highest.It consisted of 18 amino acids.Algae-bacteria biomass has great potential for application.