Hygienic effects and gas production of plastic bio-digesters under tropical conditions
ABSTRACT Plastic plug-flow bio-digesters have been promoted as a good option for improved treatment of manure and wastewater in developing countries although minimal information has been published on their hygienic status. This bench-scale study replicates bio-digester conditions to evaluate the reduction of pathogen and indicator microorganisms at three different hydraulic retention times (HRT) in the anaerobic treatment of pig manures at 30 degrees C for 50 days. Results showed that physicochemical values differed between HRTs. Gas production efficiency was better for longer HRTS. The accumulated sludge at the reactor's base increased with longer HRT. Phages and bacteria examined were reduced, but none was completely eliminated. Log10 reduction of bacteria ranged from 0.54 to 2.47. Phages ranged from 1.60 to 3.42. The reduction of organisms at HRT = 30 days was about one log10 unit higher than HRT = 15 days and about two log10 units higher than HRT = 3 days. The results indicate that the reduction of tested organisms increases with HRT. However the hygienic quality of the liquid effluent does not meet required quality values for surface and irrigation water. Longer HRTs are recommended to increase gas yield and achieve higher pathogen reduction. More barriers should be applied while handling bio-digester outputs to minimise risks to environmental and human health.
- SourceAvailable from: Annika Nordin[Show abstract] [Hide abstract]
ABSTRACT: Safe reuse of plant nutrients from human excreta increases the sustainability of society and promotes health, both by decreasing disease transmission and by increasing agricultural production. This thesis examined ammonia sanitisation as a treatment method to produce a hygienically safe fertiliser from source-separated urine and faeces. Salmonella spp. and E. coli O157:H7 were inactivated to a high degree even at low NH3 concentrations and temperatures. It was possible to model Salmonella spp. inactivation using these two parameters. Salmonella spp. inactivation is suggested to be verified by determining inactivation of faecal coliforms. Between NH3 concentrations 20 and 60 mM, a sharp decrease in inactivation was observed at 24 ºC or below for Enterococcus spp., bacteriophages and Ascaris eggs, with insignificant inactivation of the latter during 6 months. Urine contains sufficiently high total ammonia concentration and pH for selfsanitisation. Keeping the urine as concentrated as possible proved critical in achieving NH3 concentrations that inactivated Ascaris eggs. Sun exposure increased urine temperature and NH3 and shortened treatment time, and is feasible when urine containers are small. Urea treatment of faeces increased pH and total ammonia concentrations, both contributing to formation of NH3. The final value and stability of the pH achieved depended on initial pH and other material properties, but increased with increasing urea addition. At high pH caused by ash addition, urea was not degraded. When urea was added alone, it could not be confirmed that it was fully degraded. Organism inactivation was always faster in urea-treated faeces compared with untreated faeces. Urea treatment substantially shortened treatment time compared with storage, especially at the higher temperatures studied (24 and 34 ºC). Sanitation systems that collect urine and faeces separate and sanitise them by ammonia permit a high degree of hygienically safe plant nutrient reuse.
Article: Pathogens in septage in Vietnam[Show abstract] [Hide abstract]
ABSTRACT: Septage is widely acknowledged as a major source of infectious pathogens while disposal of septage, and the operation and maintenance of septic tanks, is not regulated in many developing countries. Twenty untreated septage and septage sludge samples were taken from Can Tho City, Vietnam to examine their pathogen content, and indicator micro-organisms. Escherichia coli and Enterococcus spp. were detected in all samples, regardless of sludge storage time. Phages were detected in 80% of samples. Salmonella spp. were detected in 70% of the untreated septage and 60% of septage sludge samples. Concentrations of phages and bacteria tested in septage sludge after many years of tank storage were much higher than the expected levels. Helminth ova were present in 95% of untreated septage samples with an average of 450 oval(-1), and were detected in all septage sludge samples with an average of 16,000 oval(-1). Twelve varieties of helminth ova were identified. More helminth ova varieties in higher concentrations were found in septage than those reported from stool samples. The varieties' frequency ranged from 10% to 50% and Ascaris lumbricoides predominated. Results show that pathogens and indicator micro-organisms, especially helminth ova, accumulate in sludge. Thus helminth ova should be considered when septage sludge is treated and used for agriculture. Proper health protection measures must be applied for people handling septage.Science of The Total Environment 02/2010; 408(9):2050-3. DOI:10.1016/j.scitotenv.2010.01.030 · 4.10 Impact Factor