Anaerobic Fermentation Of Waste Activated Sludge With Calcium Compounds Adjustment To Enhance Extraction Of SCFAs By LDHs

Short chain fatty acids?SCFAs?in anaerobic fermentation liquid?AFL?of waste activated sludge?WAS?are considered as an ideal carbon source for biological denitrification.However,there are lots of ammonia in AFL,which could increase the load of nitrogen removal and decrease the utilization efficiency of carbon source.Luckily,the early satge of research gourp extracted SCFAs anions successfully from AFL by in stiu synthesis of layered double hydroxides?LDHs?to achieve the separation of C and N in the simulated system.Meanwhile,the SCFAs-LDH as an external carbon source for denitrification were demonstrated feasiblly.However,the extraction efficiency of SCFAs by LDHs was much lower than the expected.Inorganic inteferring anions(CO₃^2-and PO₄^3-)in AFL had a stronger affinity with LDHs interfering SCFAs intercalation.Besides,the SCFAs concentration of WAS under AF without the addition of drug was low,which was positively related to the SCFAs extraction.To solve the problem of low extraction efficiency of SCFAs from AFL by LDHs,the anaerobic fermentation of sludge with calcium-containing compounds?eg.,calcium peroxide,mixture of sodium hydroxide and calcium hydroxide?adjustment were innovatively proposed.Calcium peroxide pretreatment of WAS to promote the SCFAs production,to increase the removal of inorganic interfering anions,and to improve extraction efficiency of SCFAs by LDHs were investigated.Alkaline fermentation of WAS with mixture of sodium hydroxide and calcium hydroxide adjustment was investigated their effects on SCFAs yield,release of inorganic interfering anions,and extraction efficiency of SCFAs by LDHs.The main fingdings and conclusions are as follows:?1?The optimal condition of p H and calcium dosage to pretreat AFL for removing carbonate were investigated.Results of experiment showed that,with a calcium dosage of 0.06 mol/L at p H 12,the removal efficiency of carbonate was up to 76.6%.By co-precipitation method to synthesize LDHs for extracting SCFAs from AFL,the SCFAs content of SCFAs-LDH-Ca was improved to 46.5 mg COD/g LDH,which was4.5-fold of the control?10.4 mg COD/g LDH?,suggesting that preteating AFL with calcium was an effective method to remove the negative effect of carbonate on the improvement of SCFAs extraction by LDHs.?2?0.3 g/g VSS of calcium peroxide?Ca O₂?pretreatment of WAS to enhance the SCFAs content of SCFAs-LDH was proposed.The experimental results revealed that the SCFAs produciotn was increased to 271.1 mg COD/g VSS in AFL of the WAS with Ca O₂ pretreatment,which was 1.5-fold of the control?180.7 mg COD/g VSS?.Meanwhile,compared with the control,the removal efficiency of phosphate and carbonate ions were up to 85.3%and 90.8%,respectively.With a higher of SCFAs production and inorganic anions removal,the SCFAs content of SCFAs-LDH-Ca O₂was improved to 26.6 mg COD/g LDH,which was 39.3%higher than that of the control.The economic analysis of using SCFAs-LDH-Ca O₂as carbon source for denitrification in wastewater was 0.9 Renminbi/m³,which led to a savings of approximately 57.0%compared with the SCFAs-LDH-Control.?3?The optimal mixture of sodium hydroxide and calcium hydroxide was 25/75that was adjusted alkaline fermentation of WAS.The experimental results showed that the SCFAs production was improved to 246.1 mg COD/g VSS,which was 57.5%higher than that of the control.At the same time,the removal efficiency of carbonate and phosphate were 71.9%and 99.4%,respectively.With inorganic anions being effectively removed and a higher SCFAs yield,the SCFAs content of SCFAs-LDH-Mixture was increased to 52.3 mg COD/g LDH,which was 2.8-fold of the control?18.9 mg COD/g LDH?.Thus,the extraction efficiency of SCFAs from WAS with mixture of sodium hydroxide and calcium hydroxide adjustment by LDHs was enhanced.