Characterization of the physicochemical composition of anaerobically digested (digestate) high throughput red meat abattoir waste in South Africa and the determination of its quality as a potential biofertilizer

Anaerobic digestion as a treatment option for waste produced in high throughput red meat abattoirs in South Africa is now gaining interest in both private and government sectors. The resultant digested slurry (digestate) is currently being regarded as waste despite its nutritional value for soil and plants which can be harnessed if digestate is utilized as biofertilizer to ensure nutrient cycling. The study investigated the physicochemical and microbial characteristics of digestate emanating from anaerobic digestion of red meat abattoir waste in South Africa, as well as evaluating its potential use as biofertilizer. The pH, total solids, volatile solids, chemical oxygen demand, electrical conductivity, total volatile fatty acids and chemical composition were determined using standard methods. Microbial analyses were determined according to the serial dilution method (10(1)- 10(10)). The results were benchmarked with Public Available Specifications (PAS) 110 standards for quality control of digestate intended to be used as biofertilizer for agricultural purposes. Results for pH, total solids, electrical conductivity, chemical oxygen demand, and total volatile fatty acids fell within the required PAS110 standard which requires standard limits of 6.5–9, 30 %–50 %, <1500 mg/L, <3000 μS/cm, and 0.43 COD/g VS respectively. Moisture content in all red meat abattoir digestate ranged from 92.05 ± 0.5 % to 95.49 ± 0.38 % and did not meet the required limit of <35 %. E. coli in untreated cattle and pig abattoir digestate were 1023 ± 35 cfu/mL and 1068 ± 51 cfu/mL, respectively, and also did not meet the required standard limit of <1000 cfu/mL. Chemical composition showed that abattoir digestate was abundant in both macronutrients and micronutrients, and heavy metal concentrations in all digestate samples fell within the PAS 110. In conclusion, abattoir digestate was observed to be highly abundant in nutrients essential for soil health and plant growth, and mostly met the required EU PAS110 standard for utilization as biofertilizer in agricultural land.