Impact Of Salinity On Lactic Acid Production From Co-fermentation Of Food Waste And Waste Activated Sludge

In recent years,bio-refinery of food waste and waste activated sludge to high value added chemicals,such as lactic acid has caught growing attention.Lactic acid is widely used precursor for biodegradable plastic and also an important industrial intermediate,mainly produced by bio-valorization of food waste and waste activated sludge?WAS?.Hence lactic acid fermentation by utilization of food waste and waste activated sludge has benefits,not just organic waste resource utilization,but also maximize the added value of fermentation products.Similarly this investigation found that many microorganisms are present in food waste fermentation and waste activated sludge's that have synergetic effects on the fermentation of lactic acid.Salt is present in food and effects the lactic acid bacteria which is yet to be investigated.The aim of dosage was to know the impact of salt on lactic acid production and to illustrate the effects of salt on intermediate metabolites in the system.The main results were as follow;Firstly,the impact of salt concentration on co-fermentation of lactic acid was studied.Experimental results showed that the effects of Na Cl on lactic acid production was dosage dependent.Three batches were conducted to investigate different concentrations of salt on co-fermentation.Blank,Na Cl-5,Na Cl-10,Na Cl-15,Na Cl-20,Na Cl-25,Na Cl-30,Na Cl-40 and Na Cl-50 g represents the concentrations of salt amended in the fermentation reactors in COD/L.The maximal concentration of lactic acid in each batch was Na Cl-25?35.23 g COD/L?and optical activity?OA?of L-lactic acid was 84.13%at 4 d in first Batch,Na Cl-25?39.78 g COD/L?and OA of L-lactic acid was 97.51%at 6 d in 2^nd batch,while at 4 d of fermentation time more production of total lactic acid was found in Na Cl-10?21.01 g COD/L?and OA of L-lactic acid was 92.22%,Na Cl-20?34.94 g COD/L?and OA of L-lactate was 78.80%.The result from three batches inferred that providing Na Cl in a proper dosage could enhance the production of lactic acid from co-fermentation of WAS and FW like Na Cl-10 and Na Cl-20.It should be noted that the generation of lactic acid was retarded in Na Cl-50 and produced a phenomenon of low promoting and high suppressing.Secondly,the variation of soluble carbohydrates,ammonia,VFA,enzymatic activity were elaborated.It can be seen from the results that salt caused?-glucosidase inhibitory activity.According to the results,the activity of protease was affected in the presence of salt,indicating that protease enzymatic activity was higher in Na Cl-10 as compared to Blank.Also the ammonia concentration?NH₄⁺-N?was increased with increasing salt dosage,high?NH₄⁺-N?release was found in Na Cl-50?13.89 mg/L?as compared to Blank?4.97 mg/L?on the 1^st day of fermentation.The results obtained about VFA yield was higher in Blank.However,from the5th day of fermentation,the concentration of VFA in Na Cl-40 increased with decrease of lactic acid concentration which indicates that lactic acid is converted rapidly.At the end of fermentation,acetic acid was the main components of VFA,7.63%?Blank?,6.23%?Na Cl-10?,28.6%?Na Cl-20?,64.2%?Na Cl-30?,74.6%?Na Cl-40?and 67.5%?Na Cl-50?.Further investigations of microbial community structure also revealed that the abundance and diversity of microflora were changed by Na Cl concentration.Microbial community study revealed that Na Cl-10 resulted in the proliferation of Lactobacillus which mainly produced lactic acid to44.06%at 3d of fermentation.The abundance of key microorganisms was enhanced and reduced by salt dosage.Firmicutes,Proteobacteria and Actinobacteria were respectively changed in community,which caused the difference of OA of L-lactic acid.From the Pyrosequencing data,it could be surmising that proper salt addition in Na Cl-10 escalated the particular LAB?Lactobacillus?.Furthermore,during fermentation when dosed with high concentration of salt?Na Cl-50?decrease of lactic acid bacteria?LAB?were detected with a simultaneous increase of other microbes such as Tepidibacter?36.3%?.For instance Lactobacillus culture enhanced to 44.06%in Na Cl-10 compared to Blank which is deficient in this,this means that lower dosage of salt facilitate the growth of Lactobacillus.Furthermore Enterococcus,believed to produce L-lactic acid,was also noticed in relatively higher abundance in Na Cl-30,which might be the cause of the better production of L-lactic acid.The results showed that the dominant species in the systems were affected by the addition of salt.