RESUMO
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 (101- 1010). 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.
RESUMO
Management and disposal of pig farm seepage constitute a serious environmental challenge, and seepage discharge from agricultural waste-water is considered to be one of the greatest contributors of organic substances, bacterial pathogens, and antibiotic resistance genes into the environment. The objectives of this study were to assess the level of bacteriological pollution and to identify the resident antibiotic-resistant genes of culturable bacteria from a studied pig farm seepage. Enumeration of the viable bacterial cell of plated bacteria suspensions (10-1 to 10-8 cfu/mL) was performed; also, identification of pure bacterial colonies was done using an API 20E bacterial identification kit. CLSI guidelines for antimicrobial susceptibility testing were adopted to determine the antibiotic susceptibility/resistance of the cultured bacterial isolates. Identification of resident-resistant genes was done using molecular biology procedures. The results on viable cells in seepage samples ranged from 4.30 × 102 to 1.29 × 109 cfu/mL. Pseudomonas luteola, Enterococcus vulneris, Salmonella choleraesuis spp arizonae, Escherichia coli, Enterobacter cloacae, Proteus mirabillis etc. were isolated from the pig farm soil samples. Almost all of the cultured isolates were resistant to Penicillin G, Vancomycin, Oxytetracycline, Spectinomycin, and Lincomycin. The most frequent resistant genes detected in the isolates were Van A, Van B, InuA, aph (3")-llla, blaTEM, Otr A, and Otr B. It was inferred from the study that Pig farm seepage has the ability to cause bacterial pollution that may negatively impact the natural environment, by introducing bacteria pathogens that harbor antibiotic-resistant genes.
