In modern wastewater treatment processes, the addition of carbon sources is a crucial operational step. The purpose is to promote the growth and metabolic activity of microorganisms by providing necessary organic carbon sources, thereby achieving effective removal of nutrients such as nitrogen and phosphorus from wastewater. Therefore, accurately calculating the amount of carbon source added is not only related to improving processing efficiency, but also directly affects operating costs and environmental benefits.
Basic calculation principle of 01 carbon source dosage
The calculation of carbon source dosage is mainly based on factors such as BOD5/COD ratio, denitrification rate, and total nitrogen removal required. The basic calculation formula can be expressed as: carbon source dosage (calculated as COD)=(theoretical COD required for denitrification - biodegradable COD in wastewater and raw water) × conversion coefficient. The conversion coefficient is usually determined based on actual engineering experience or laboratory simulation tests.
02 Factors affecting carbon source dosage
In the process of sewage treatment, adding carbon sources as a necessary condition for microbial growth and denitrification requires comprehensive consideration of multiple factors, including but not limited to the following:
Water quality monitoring indicators: C/N ratio (carbon nitrogen ratio): the ratio between COD (chemical oxygen demand) and total nitrogen (TN) or Kjeldahl nitrogen (TKN) in wastewater. To ensure the complete denitrification process, it is usually required to maintain a suitable C/N ratio, such as between 4:1 and 6:1, which may vary depending on the specific situation. Ammonia nitrogen content: When the ammonia nitrogen in the wastewater exceeds the standard, it is necessary to supplement the carbon source to balance the reaction system and improve the integrity of denitrification. Biological treatment stage requirements: Activated sludge cultivation and domestication stage: In this stage, microorganisms require sufficient carbon sources to promote rapid reproduction and adapt to the environment. If the carbon source in the raw water is insufficient, additional additions are needed. Denitrification process: Based on the denitrification process design, select the appropriate type and injection point of carbon source to ensure that the carbon source can be effectively utilized in the denitrification tank, avoiding loss or premature consumption.
Biodegradability of wastewater: Types of organic matter and difficulty of degradation • Different types of organic carbon sources have significant differences in the bioavailability of microorganisms. Small molecule carbon sources that are easy to degrade should be selected, and their ability to meet the metabolic needs of microorganisms under specific conditions should be considered.
Economy and safety: Carbon source cost: The selected carbon source should have high economic benefits, that is, it can achieve good treatment effects while minimizing operating costs. Storage and use safety: The added carbon sources such as methanol, acetic acid, etc. should have good storage stability and use safety to prevent leakage and environmental pollution or safety hazards.
Process control flexibility: dosing point position and method: Determine the optimal dosing point position based on the characteristics of the process flow, such as whether it is in the anoxic or anaerobic zone, and whether to adopt continuous or intermittent dosing.
Environmental impact and regulatory constraints: Secondary pollution risk: Ensure that adding carbon sources will not cause new pollutant emissions and comply with environmental regulations. Only by combining all the above factors can a scientifically reasonable carbon source addition strategy be formulated, effectively improving the imbalance of carbon sources in sewage and optimizing the performance of the entire sewage treatment system.
Method for calculating the amount of carbon source added in 03
The calculation of carbon source dosage is a crucial step in wastewater treatment, used to supplement the organic carbon required for microbial growth and promote biodegradation processes. Here are two different calculation methods: a simple calculation method based on nitrogen removal demand: when using the total Kjeldahl nitrogen (TKN) in wastewater as a reference, the following formula can be used to calculate the amount of external carbon source that must be added (calculated as chemical oxygen demand COD): Cm=20N - C, where Cm represents the amount of external carbon source that needs to be added (mg/l or kg/d, depending on the unit of V); 20 is the CN ratio, which is the theoretical mass ratio of carbon consumed per gram of nitrogen; N is the amount of Total Kjeldahl Nitrogen (TKN) that needs to be removed (mg/l or kg/d); C is the carbon source difference between the inflow and outflow, which is the difference between the available COD in the sewage treatment system and the actual required COD (mg/l or kg/d). Calculation method based on COD difference and COD contribution rate: Determine the carbon source dosage based on COD difference and COD contribution rate (applicable to a wider range of scenarios, considering inflow, outflow, and target COD values): Carbon source dosage (kg/d)=COD difference (kg/d)/COD contribution rate. Here, COD difference refers to the COD gap obtained by subtracting the actual inflow COD value from the target COD value of the treatment tank; COD contribution rate refers to the proportion of carbon sources added that can be converted into COD during the biochemical reaction process. In practical applications, the selection of appropriate calculation methods should be determined based on specific water quality parameters, process flow, and nutritional requirements of the microbial system.
