The effect of anaerobic digestion and storage on indicator microorganisms in swine and dairy manure

Abstract

The aim of this experimental study was to evaluate the influence of anaerobic digestion and storage on indicator microorganisms in swine and dairy excreta. Samples were collected every 90 days for 15 months at eight farms, four pig, and four dairy farms, four of them having a biogas plant. Moreover, to evaluate storage effects on samples, 20 l of manure and slurry taken at each farm (digested manure only in farms with a biogas plant) were stored in a controlled climatic chamber at 18 °C, for 6 months. The bacterial load and the chemical-physical characteristics of excreta were evaluated at each sampling time, stored slurry, and manure were sampled and analyzed every 2 months. A high variability of the concentration of bacteria in the different excreta types was observed during the experiment, mainly depending on the type and time of treatment. No sample revealed either the presence of Escherichia coli O157:H7 or of Salmonella, usually linked to the temporary rearing of infected animals in facilities. Anaerobic digestion and storage affected in a significant way the reduction of indicator bacteria like lactobacilli, coliforms, and streptococci. Anaerobic digestion lowered coliforms in pig slurry (- 2.80 log, P < 0.05), streptococci in dairy manure (- 2.44 log, P < 0.001) and in pig slurry (- 1.43 log, P < 0.05), and lactobacilli in pig slurry (- 3.03 log, P < 0.05). Storage lowered coliforms and the other indicators counts, in particular in fresh wastes, while clostridia did not show a reduction in concentration.

Microbial load in bio-slurry from different biogas plants in Bangladesh

“…Similar results were also reported by several researchers in other parts of the world. Costa et al [28] found the lower number of bacterial load including coliforms, lactobacillus, and streptococci after anaerobic digestion in bio-slurry samples. Philipp and Holzle [29] reported that E coli were absent when the digester was operated at 55°C.…”

Detection and occurrence of indicator organisms and pathogens

“…In a case study conducted by Elkayam et al (2017), streptococci along with other microbial indicators were used to evaluate the effectiveness of soil aquifer treatment in removing microbial contaminations. In another study, streptococci and other indicator bacteria, including lactobacilli and coliforms were quantified to assess the effect of anaerobic digestion on indicator microorganisms in swine and dairy manure (Costa et al, 2017).…”

Factors Influencing the Willingness of Dairy Farmers to Adopt Biogas Plants: A Case Study in Hokkaido, Japan

“…There should also be subsidies for their operation, such as FIT schemes (despite the difficult situation they face for power grid use). The effects of BGPs on the environment and dairy farming have already been explained in previous studies, as mentioned above [1,3,5,6,[9][10][11][12][13][14][15]. Therefore, it should be emphasized that BGPs are different from other power sources that require policy design, such as preferential grid use and support of continuous FIT schemes.…”

“…AD is normally carried out in biogas plants (BGPs), and it has several benefits. For example, it reduces biomass, alleviates adverse effects by microorganisms, and reduces undesirable odors [3,5,9,10]. In addition, it produces digestate that can be used as organic fertilizer and reduce the need for chemical fertilizers [11].…”