The survival of pathogenic bacteria and plant growth promoting bacteria during mesophilic anaerobic digestion in full‐scale biogas plants

Abstract

The introduction of biogas plants is a promising way to recycle organic wastes with renewable energy production and reducing greenhouse gas. Application of anaerobic digestate as a fertilizer reduces the consumption of chemical fertilizers. In this study, the survival of pathogenic bacteria and plant growth promoting bacteria (PGPB) in two full‐scale biogas plants operated at mesophilic condition were investigated. Feedstock and anaerobic digestate samples were collected from biogas plants and bacteria load in samples were detected using standard dilution plate method. Pathogenic bacteria were reduced to not detected level through mesophilic digestion tank except for Campylobacter. However, it could be reduced by 98.7% through a sterilization tank. Bacillus was detected at 8.00 and 7.81 log10 CFU/g dry matter in anaerobic digestates, and it was also resistant to sterilization tank. Bacillus spp. is considered to be the safe bacteria that hold remarkable abilities for promoting plant growth. The results showed that treatment at biogas plants is effective to reduce pathogenic bacteria in dairy manure, and sterilization could further reduce the sanitary risks of pathogenic bacteria relating to anaerobic digestate application. Anaerobic digestates could also be utilized as bio‐fertilizer as the high load of plant growth promoting bacteria.

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.…”

“…The amount of industrial waste generated in Hokkaido, Japan, in 2015 was recorded to be about 40 million tons, of which the proportion of livestock manure accounted for about 50% [1]. Problems caused by improper manure treatment include nitrate from undecomposed compost polluting the soil and water, poor feed (grass) produced without compost, the presence of weed seeds, the occurrence of pathogenic bacteria, and odor emissions resulting from insufficient aerobic fermentation, which reduces the quality of life in neighboring communities and impacts human health (e.g., headaches and eye and nose irritation) [2][3][4][5][6][7][8].…”

“…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].…”

Improved biofertilizer properties of digestate from codigestion of brewer’s spent grain and palm oil mill effluent by manure supplementation

“…Moller and Muller [44] reported an increase in concentrations of NH 4 -N by 45 to 80% following AD. Likewise, Coelho and other authors recorded an increase in concentration of macronutrients [33,39]. Like nitrogen, phosphorus may be present in organic or inorganic form in anaerobic digestate.…”

“…This marked reduction was statistically significant (p < 0.05) ranging from 0.4 to 1.0 log CFU mL − 1 thus substantiating the earlier report of Alfa et al [15] who recorded similar trends for coliform count and fungal count. However, Qi et al [39] recorded a 100% reduction in all indicator and pathogenic bacteria. These results indicate that laboratory-scale reactors may be less efficient in pathogen reduction than full-scale biogas plants.…”