Fermentation method for recovering carboxylic acids while reducing greenhouse gas emissions

A fermentation method for recovering carboxylic acids while reducing greenhouse gas emissions, comprising the following steps:

• step 1, installing a fermentation device for recovering the carboxylic acids while reducing the greenhouse gas emissions on a ground close to a sewage treatment facility, wherein the fermentation device comprises a fermentation container (1), and a sludge inlet assembly (2), a decanting assembly (3), a hydraulic circulation assembly (4), a heating and insulation assembly (5), an agitator assembly (6), a reagent regulation assembly (7), and a monitoring and electrical control assembly (9) mounted on the fermentation container (1);
• step 2, conveying, by using the sludge inlet assembly (2) connected to a lower part of the fermentation container (1), sludge to be treated into the fermentation container (1), wherein the sludge to be treated is primary sludge or surplus sludge generated by the sewage treatment facility;
• step 3, drawing and recirculating, by using the hydraulic circulation assembly (4), the sludge to be treated inside the fermentation container (1) to agitate the sludge to be treated and improve a hydraulic circulation flow state of the sludge to be treated;
• heating and insulating the sludge to be treated inside the fermentation container (1) via the heating and insulation assembly (5);
• fully agitating, by using the agitator assembly (6), the sludge inside the fermentation container (1) after the heating and insulating to ensure a uniform quality distribution of the sludge inside the fermentation container (1);
• and delivering, by using the reagent regulation assembly (7), reagents into the fermentation container (1) to regulate a growth and metabolic environment of microorganisms in the sludge inside the fermentation container (1);
• step 4, continuously monitoring, via the monitoring and electrical control assembly (9), a temperature, a potential of hydrogen (pH) value, and water quality of the sludge inside the fermentation container (1) to obtain monitoring results, and regulating in real time, based on the monitoring results, process parameters of the sludge inlet assembly (2), the hydraulic circulation assembly (4), the heating and insulation assembly (5), the agitator assembly (6), and the reagent regulation assembly (7) to ensure that the fermentation device is in optimal operating conditions and produces the carboxylic acids at a predetermined concentration, wherein the optimal operating conditions comprise:
• a fermentation residence duration of the sludge inside the fermentation container (1) in a range of 5 days (d) to 8 d;
• the temperature of the sludge inside the fermentation container (1) maintained stable in a range of 35° C. to 55° C. with the uniform quality distribution of the sludge;
• the pH value of the sludge inside the fermentation container (1) maintained in a range of 8 to 10;
• and concentrations of trace elements in the sludge inside the fermentation container (1) as follows:
• copper (II) ion (Cu2+) in a range of 20 millimoles per liter (mmol/L) to 65 mmol/L, manganese (II) ion (Mn2+) in a range of 2.5 mmol/L to 6.0 mmol/L, boron (III) ion (B3+) in a range of 15.0 mmol/L to 28.5 mmol/L, molybdenum (VI) ion (Mo6+) in a range of 4.0 mmol/L to 6.2 mmol/L, wolframium (VI) ion (W6+) in a range of 7.0 mmol/L to 12.2 mmol/L, nickel (II) ion (Ni2+) in a range of 3.0 mmol/L to 5.5 mmol/L, cobalt (II) ion (Co2+) in a range of 10.0 mmol/L to 18.3 mmol/L, zinc ion (Zn2+) in a range of 25.5 mmol/L to 35.0 mmol/L, and calcium ion (Ca2+) in a range of 10.5 mmol/L to 30.5 mmol/L;
• and
• step 5, decanting, through the decanting assembly (3), carboxylic acid clarified liquid produced by fermentation from a top of the fermentation container (1), and conveying the carboxylic acid clarified liquid to a biological reaction tank of the sewage treatment facility, thereby promoting a denitrification and phosphorus removal process,
• wherein a calculation formula for a concentration Sv of the carboxylic acids produced in the fermentation container (1) is expressed as follows:
• S
• v
• =
• ∫
• [
• N
• 1
• +
• aN
• 2
• N
• 1
• +
• N
• 2
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• ⁢
• dt
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• =
• ∫
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• ⁢
• dt
• S
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• =
• ∫
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• N
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• where Sv represents the concentration of the carboxylic acids, measured as chemical oxygen demand (COD);
• Sp represents a concentration of organic matter in the sludge to be treated, measured as COD;
• Sh represents a concentration of reaction hydrolysis products, comprising concentrations of protein, fat, and carbohydrate, measured as COD;
• N1 represents a variable frequency output power of a circulation pump (41) for hydraulic agitation;
• N2 represents a variable frequency output power of an agitator (61) for mechanical agitation;
• a represents a regulation coefficient of agitation intensity of the agitator (61);
• km,h represents a maximum specific utilization rate of the reaction hydrolysis products;
• Xh represents a microbial concentration of carboxylic acid-producing bacteria;
• KS,h represents a half-saturation constant for growth of the carboxylic acid-producing bacteria;
• KI,h represents an influence coefficient of the concentration of the carboxylic acids on the growth of the carboxylic acid-producing bacteria;
• km,v represents a maximum specific utilization rate of the carboxylic acids;
• Xv represents a microbial concentration of methanogenic bacteria;
• k represents a maximum specific substrate removal rate constant;
• kd,h represents a microbial endogenous decay rate of the carboxylic acid-producing bacteria;
• and kd,v represents a microbial endogenous decay rate of the methanogenic bacteria;
• and
• wherein the monitoring and electrical control assembly (9) is configured to calculate the concentration of the carboxylic acids produced in the fermentation container (1) using the above calculation formulas based on the process parameters, or dynamically regulate the process parameters of the fermentation device based on the predetermined concentration of the carboxylic acids.