Filamentous bulking related to organic acids can be a problem in wastewater systems.
Organic acids are formed under anerobic conditions where bacteria grow under what we call fermentative conditions (bacteria using organic compounds as a terminal electron acceptor to get energy). Common sources of organic acids include – collection systems, equalization tanks, sludge layers in lagoons, and even anaerobic digesters. If there are sulfides present, organic acids are a key part of what we call “septic” water. Biological nutrient removal systems require organic acids to function properly – especially in the case of phosphorus removal. At the same time, organic acids can also be a problem component in wastewater operations. Here's how organic acids contribute to these processes:
Source of Carbon and Energy for Microorganisms:
Organic acids serve as a crucial carbon source for microorganisms in biological treatment systems. Microorganisms use organic acids as a substrate for their growth and metabolism. This is particularly important in aerobic treatment processes like activated sludge, where microorganisms need organic carbon to thrive.
Microbial Metabolism and Nutrient Removal:
Microorganisms metabolize organic acids through various biochemical pathways, contributing to the breakdown of complex organic compounds. This metabolism results in the production of microbial biomass and energy for microbial activities. As microorganisms grow and reproduce, they assimilate nutrients, aiding in the removal of nitrogen and phosphorus compounds from the wastewater.
In the case of Bio-P organisms, the microbes uptake organic acids under anaerobic conditions which are utilized later under aerobic conditions. Energy is then stored as intracellular phosphate which also powers the uptake of organic acids under anaerobic conditions. Organic acids also are often the soluble carbon source for denitrification.
Encourage Filamentous Growth:
High organic acids can depress D.O. levels in the influent zone of activated sludge systems. The low D.O. coupled with soluble substrate creates conditions favoring several types of common filamentous bulking organisms. Preventing the low D.O. zone with high organic acids, is why step feed systems are often effective in controlling bulking in plug flow systems.
pH Buffering:
Organic acids can act as natural pH buffers in wastewater systems. In biological treatment processes, the production of organic acids by microbial activity can help maintain a suitable pH environment for the microorganisms. This is crucial because microbial activity is often sensitive to changes in pH, and maintaining an optimal pH range is necessary for efficient treatment.
Enhancement of Anaerobic Digestion:
In anaerobic digestion processes, organic acids are intermediates in the breakdown of complex organic matter. Later, archaea methanogens convert organic acids into methane and carbon dioxide. The production of organic acids is a key step in the hydrolysis and acidogenesis phases of anaerobic digestion.
Inhibition and Toxicity:
On the flip side, excessive accumulation of certain organic acids can have inhibitory effects on microbial activity. Some organic acids, especially those with low pH values, can be toxic to microorganisms and may impact the efficiency of the treatment process. Therefore, it's essential to carefully manage the concentration and types of organic acids in the wastewater.
Formation of Extracellular Polymeric Substances (EPS):
Microorganisms in biological treatment systems produce extracellular polymeric substances (EPS), which play a role in the formation and stability of biofilms. These substances, which include organic acids, help in the adhesion of microbial communities to surfaces, promoting the formation of biofilms in biofilm-based treatment systems. Excessive organic acids can also trigger over-production of EPS leading to non-filamentous or Zoogleal bulking.
Source of Carbon and Energy for Microorganisms:
Organic acids serve as a crucial carbon source for microorganisms in biological treatment systems. Microorganisms use organic acids as a substrate for their growth and metabolism. This is particularly important in aerobic treatment processes like activated sludge, where microorganisms need organic carbon to thrive.
Microbial Metabolism and Nutrient Removal:
Microorganisms metabolize organic acids through various biochemical pathways, contributing to the breakdown of complex organic compounds. This metabolism results in the production of microbial biomass and energy for microbial activities. As microorganisms grow and reproduce, they assimilate nutrients, aiding in the removal of nitrogen and phosphorus compounds from the wastewater.
In the case of Bio-P organisms, the microbes uptake organic acids under anaerobic conditions which are utilized later under aerobic conditions. Energy is then stored as intracellular phosphate which also powers the uptake of organic acids under anaerobic conditions. Organic acids also are often the soluble carbon source for denitrification.
Encourage Filamentous Growth:
High organic acids can depress D.O. levels in the influent zone of activated sludge systems. The low D.O. coupled with soluble substrate creates conditions favoring several types of common filamentous bulking organisms. Preventing the low D.O. zone with high organic acids, is why step feed systems are often effective in controlling bulking in plug flow systems.
pH Buffering:
Organic acids can act as natural pH buffers in wastewater systems. In biological treatment processes, the production of organic acids by microbial activity can help maintain a suitable pH environment for the microorganisms. This is crucial because microbial activity is often sensitive to changes in pH, and maintaining an optimal pH range is necessary for efficient treatment.
Enhancement of Anaerobic Digestion:
In anaerobic digestion processes, organic acids are intermediates in the breakdown of complex organic matter. Later, archaea methanogens convert organic acids into methane and carbon dioxide. The production of organic acids is a key step in the hydrolysis and acidogenesis phases of anaerobic digestion.
Inhibition and Toxicity:
On the flip side, excessive accumulation of certain organic acids can have inhibitory effects on microbial activity. Some organic acids, especially those with low pH values, can be toxic to microorganisms and may impact the efficiency of the treatment process. Therefore, it's essential to carefully manage the concentration and types of organic acids in the wastewater.
Formation of Extracellular Polymeric Substances (EPS):
Microorganisms in biological treatment systems produce extracellular polymeric substances (EPS), which play a role in the formation and stability of biofilms. These substances, which include organic acids, help in the adhesion of microbial communities to surfaces, promoting the formation of biofilms in biofilm-based treatment systems. Excessive organic acids can also trigger over-production of EPS leading to non-filamentous or Zoogleal bulking.
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