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According to a United Nations report, by the year 2025 milk production will increase by 177 million tonnes. The growth of the dairy industry means increasing levels of dairy effluent, which without proper treatment can have negative impacts on environmental health. The use of bioaugmentation strategies to increase the effectiveness and efficiency of wastewater treatment could help curb the negative effects of increasing dairy industry growth.

Challenges

The challenge in dairy wastewater treatment is to reduce the chemical oxygen demand (COD) of the effluent without excess sludge production from the increased organic matter content of the wastewater. Proper treatment will reduce the COD to levels compliant with local standards and low enough to prevent environmental damages. Improper dairy effluent treatment can lead to decreases in surface water quality and increased nitrate levels. Elevated nitrate levels have been linked to eutrophication in water bodies such as lakes and rivers. Additionally, elevated nitrate levels in drinking water supplies specifically are linked to stomach cancer and methemoglobinemia (blue baby syndrome) in infants.

Processes

It has been shown that using mixed fungal consortiums in conjunction with traditional microbial components is effective in reducing final biomass concentration in dairy wastewater, indicating a reduction in total sludge produced in the bioreactor. The addition of Aspergillus niger, Mucor hiemalis, and Galactomyces geotrichum at an inoculum ratio of 3.3% was found to increase the effectiveness of the degradation of organic matter, thus reducing sludge, compared to the bioreactor composition without bioaugmentation. Aspergillus niger, Mucor hiemalis, and Galactomyces geotrichum produce enzymes able to degrade animal byproducts of fat and oil.

Process of Fungi Inoculation

Fungi selected to be used for bioreactor tank inoculation are introduced to a culture medium of synthetic dairy wastewater. Synthetic dairy wastewater is made with diluted milk and sweet whey powder. This fungi inoculum can then be added to the bioreactor at a ratio of 3.3%, or 33mL for every 1L of wastewater. By aerating and agitating the fungal culture, the inoculation can be accelerated, yielding a faster startup of the bioreactor and increasing biodegradation efficiency.

Biofilm Development

The critical stage in the set up of dairy wastewater treatment processes is the development of biofilm in the bioreactors and its stabilization. Bioaugmentation with commercially available microbes improves biofilm development and stabilization by shortening the start-up process, and thereby improving efficiency of dairy wastewater treatment. Modification of traditional sequencing batch biofilm reactors (SBR) using a plastic media to increase surface area increases biofilm development and increasing the total biofilm mass. Bioreactors with greater total biofilm mass are more efficient at degrading dairy wastewater with increased organic content and produce less bio-sludge.

Plackett-Burman Assay

The Plackett-Burman experimental design statistically separates potentially compounding variables to find two-factor interactions that occur. Application of the Plackett-Burman Assay in bacterial consortiums composed of bacteria selected to degrade dairy wastewater has shown that when compared to combinations of bacterial strains, bacterial consortiums degraded wastewater more completely and in less time (degradation standardized to COD removal). The statistical models generated by Plackett-Burman assays can be used to predict outcomes of bioreactor systems, allowing for more effective bioreactor design.