Effect of Solids Retention Time on the Denitrification Potential of Anaerobically Digested Swine Waste

Three continuously stirred tank reactors (CSTR) were operated in semi continuous mode treating swine waste using anaerobic digestion. The reactors were used to test the effect of solid retention time (SRT) on CH4 yield, total ammonia nitrogen (TAN) concentrations, % volatile solids (VS), chemical oxygen demand (COD) and volatile fatty acids (VFA) removal, readily biodegradable COD concentration and the denitrification potential for the effluent in a biological nutrient removal (BNR) system. During Phase I of the study, the three reactors were operated at the same 28 day SRT for 16 weeks. SRTs were then changed during the 12 week Phase II period. The SRTs studied were 14, 21 and 28 days, with the same organic loading rate (OLR) of 1.88 ± 0.2 kg VS/ m3-day. The reactor with the lowest SRT (14 days) had the highest VS and VFA removal at 73.6 and 67.6% and lowest TAN concentration at 0.78 g NH4+-N/L, followed by the 21 day and 28 day reactors. This was likely due to the fast microbial growth rates and substrate utilization rates in this reactor compared with the other two. The 14 day reactor had the highest CH4 yield at 0.33 m3CH4/kg VS added and readily biodegradable COD concentration at 0.93 COD/L. The variations in CH4 yield and readily biodegradable COD concentrations between the three reactors were not statistically significant. Denitrification potential for the reactors was 1.20, 0.73 and 0.56 g COD/g N for 14, 21 and 28 day reactors, respectively, and the differences were statistically significant. None of the reactors achieved a denitrification potential of 5 g COD/g N, the amount required to use effluent of anaerobically digested swine waste as an internal carbon source in a BNR. This was attributed to operating conditions such as freezing and thawing of the raw swine waste that maximized CH4 yield and lowered the readily biodegradable COD concentration. In addition the 14 day reactor had low TAN concentrations thus increasing the denitrification potential of the centrate from that reactor

Energy Production and Effluent Quality in Tubular Digesters Treating Livestock Waste in Rural Costa Rica

Use of tubular anaerobic digesters to treat livestock waste in developing countries has energy, agricultural, health, social and environmental benefits. However, careful use of digester effluent as a soil amendment is required due to the potential presence of protozoan parasites Cryptosporidium parvum and Giardia lamblia. This research investigated the performance of four tubular digesters in the Monteverde region of Costa Rica. High (\u3e75%) volatile solids and BOD5 removal efficiencies were observed, which was attributed to the formation of a biologically active floccular sludge layer. Computational fluid dynamics (CFD) and bioprocess models were developed to evaluate the transport and transformation mechanisms in the digesters. The CFD model estimated a mean liquid hydraulic residence time (HRT) of 23 days and the bioprocess model estimated an average mean cell residence time (MCRT) of 115 days. Cryptosporidium parvum and Giardia lamblia inactivation studies were performed in the laboratory under conditions similar to the environmental conditions observed in the field tubular digesters. The environmental conditions included: ambient temperatures (21-24°C), neutral pH and total ammonia nitrogen (TAN) concentrations below 250 mg NH4+-N/L. Inactivation rate constants for Cryptosporidium parvum and Giardia lamblia were 0.056 and 0.726 day-1, respectively. An (oo)cysts solid-liquid phase distribution study indicated that 70% of both (oo)cysts adhered to biosolids. A tubular digester model was used to estimate the concentration of viable (oo)cysts in the digester effluents. (Oo)cysts adhesion to solids, total solids concentration in the digester and HRT were the main factors contributing to the modeled effluent concentration of viable (oo)cysts. Since the model predicted presence of viable (oo)cysts in the tubular digester effluent, a quantitative microbial risk assessment (QMRA) model was developed to estimate the risk of infection from exposure to raw livestock waste and tubular digester effluents in two rural communities in Costa Rica. The risk of infection from Cryptosporidium parvum and Giardia lamblia was assessed for occupational and public exposure pathways; fomite and soil contamination and crop contamination from runoff. Results from the QMRA indicated that the concentration of (oo)cysts in the raw livestock waste, inactivation rates at the various exposure pathways and the treatment of livestock waste were the main contributing factors to the risk of infection. This research indicated that treatment of livestock waste in tubular digesters significantly decreased the risk of infection to below WHO’s acceptable individual annual risk of infection (10-4). This is the first study to combine mathematical modeling with field studies to determine the physical and biological processes in tubular digesters. This is also the first study to combine mathematical models with field and laboratory studies to determine the concentration of (oo)cysts in tubular digester effluents and to predict the risk of infection from Cryptosporidium parvum and Giardia lamblia if tubular digester effluent is used as a soil amendment

Challenges for consent and community engagement in the conduct of cluster randomized trial among school children in low income settings: experiences from Kenya.

BACKGROUND: There are a number of practical and ethical issues raised in school-based health research, particularly those related to obtaining consent from parents and assent from children. One approach to developing, strengthening, and supporting appropriate consent and assent processes is through community engagement. To date, much of the literature on community engagement in biomedical research has concentrated on community- or hospital-based research, with little documentation, if any, of community engagement in school-based health research. In this paper we discuss our experiences of consent, assent and community engagement in implementing a large school-based cluster randomized trial in rural Kenya. METHODS: Data collected as part of a qualitative study investigating the acceptability of the main trial, focus group discussions with field staff, observations of practice and authors' experiences are used to: 1) highlight the challenges faced in obtaining assent/consent; and 2) strategies taken to try to both protect participant rights (including to refuse and to withdraw) and ensure the success of the trial. RESULTS: Early meetings with national, district and local level stakeholders were important in establishing their co-operation and support for the project. Despite this support, both practical and ethical challenges were encountered during consenting and assenting procedures. Our strategy for addressing these challenges focused on improving communication and understanding of the trial, and maintaining dialogue with all the relevant stakeholders throughout the study period. CONCLUSIONS: A range of stakeholders within and beyond schools play a key role in school based health trials. Community entry and information dissemination strategies need careful planning from the outset, and with on-going consultation and feedback mechanisms established in order to identify and address concerns as they arise. We believe our experiences, and the ethical and practical issues and dilemmas encountered, will be of interest for others planning to conduct school-based research in Africa. TRIAL REGISTRATION: National Institute of Health NCT00878007

Bio-optimization of compost with cultures of mountain microorganisms (MM) and digested sludge from bio-digester (LDBIO)

El compost es un abono orgánico que puede aportar nutrientes, materia orgánica, humedad y microorganismos benéficos al agroecosistema. La calidad del compost depende en gran medida de las características de los materiales que se empleen en el proceso de elaboración, por lo que uno de los retos existentes en la tecnología del compostaje es la optimización de la calidad del material terminado. Los MM son inóculos microbianos con altas poblaciones principalmente de hongos, bacterias y actinomicetos que se encuentran naturalmente en el suelo, mientras que los LDBIO son los sólidos precipitados resultantes del proceso de digestión anaeróbica. El empleo de MM y LDBIO como agentes optimizadores de la calidad del compost no ha sido estudiado. El presente trabajo tiene como objetivo investigar, en forma no experimental, económica, y a un nivel de resolución macro utilizan-do pruebas de laboratorio robustas, si el MM y LDBIO poseen características favorables como agentes efectivos para la optimización del compost, e identificar la combinación de estos materiales que permita producir compost de mayor calidad. De acuerdo con los datos obtenidos, se logra evidenciar a ese nivel de resolución, que efectivamente los MM y LDBIO presentan características apropiadas como agentes optimizadores del compost. El compost que presenta las mejores características de calidad en cuanto a la concentración de macronutrientes, contenido de materia orgánica, carbono, retención de humedad y concentración de biomasa microbiana, es el que contiene MM y LDBIO en forma integrada. La incorporación de estos compuestos no afecta otros parámetros de calidad de este abono, incluyendo el pH, la CE y la relación C/N. Tampoco afecta la capacidad de maduración, la estabilidad y la inocuidad del compost final, por lo que se concluye que es factible continuar invirtiendo en la investigación de estos compuestos como agentes optimizadores del compost. Se recomienda realizar ensayos de respuesta de crecimiento con el abono optimizado para identificar el potencial de aporte al desarrollo de los cultivos.Compost is a bio-fertilizer that contains nutrients, organic matter, water and microorganisms that benefit the integrity of agroecosystems. Compost quality is highly dependent on the characteristics of the materials employed in production. One of the main challenges in compost technology is quality optimization. MM are microbial cultures containing dense populations of native soil microorganisms including bacteria, fungi and actinomycetes. LDBIO are the precipitated solids found in anaerobic reactors. This is a low cost, non-experimental, economic, low resolution pre-feasibility study that uses robust laboratory analytical methods to identify whether these compounds can be used as compost optimization agents, and identify the combination of these materials that produce the highest quality compost. According the re-sults obtained, there is empirical evidence that MM and LDBIO have potential as compost optimization agents. The compost with the best quality characteristics (macronutrient concentration, organic matter, carbon and water content, microbial biomass) is the one that contains both MM and LDBIO. The incorporation of these materials in the com-post does not affect other compost quality parameters such as pH, EC and C/N ratio. It does not affect the maturity, stability and innocuity of compost. Therefore, at this level of resolution, it is concluded that it is feasible to continue researching these materials as compost optimiza-tion agents. It is recommended to implement plant growth-response tests in order to identify the potential of the optimized compost to enhance plant development.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Agroalimentarias::Centro de Investigaciones Agronómicas (CIA

Fitotoxicidad de compost producido con cultivos de microorganismos de montaña y lodos digeridos de biodigestor

Introduction: compost quality may be enhanced with compost optimization agents. These agents must guarantee safety. Compost phytotoxicity tests are an economic, rapid and reliable mechanism to detect toxic substances in compost that may inhibit seed germination and plant growth. Objective: to evaluate the phytotoxicity of mountain microorganisms and biodigester sludge as compost optimization agents Methods: complete randomized blocks bioassay with cucumber seeds (Cucumis sativus). Results: individual use of these agents has no inhibitory effects in cucumber germination and growth and is thus safe. However, added simultaneously, they have inhibitory effects on germination and growth of cucumber, possibly from the phytotoxic effect of excess Zinc and Boron. Conclusion: we recommend caution and further tests with additional growth stages and species.Introducción: la calidad del compost puede ser ajustada a través de la incorporación de agentes optimizadores. La selección de los agentes debe hacerse en forma cuidadosa para efectos de garantizar la seguridad del compost maduro. Las pruebas de fitotoxicidad son un mecanismo económico, rápido y confiable para detectar en el compost la presencia de sustancias tóxicas inhibidoras de la germinación y el crecimiento de cultivos. Objetivo: evaluar la fitotoxicidad de los microorganismos de montaña y los lodos de biodigestor como agentes optimizadores del compost. Métodos: bioensayo de germinación y crecimiento de semillas de pepino (Cucumis sativus) utilizando un arreglo de bloques completamente aleatorizados. Resultados: el empleo individual de estos agentes, no tiene un efecto inhibidor en la germinación y el crecimiento del pepino, por lo que pueden ser considerados como materiales seguros para la optimización de la calidad del compost. Sin embargo, la incorporación simultánea de ambos agentes en la producción de este abono orgánico provocó una disminución significativa en la germinación y el crecimiento inicial del pepino. Este resultado podría explicarse por el efecto fitotóxico que ejerce el exceso de Zinc y Boro detectado en el compost que combina ambos materiales. Conclusión: recomendamos utilizar este compost con precaución y llevar a cabo otras pruebas de crecimiento para identificar si la fitotoxicidad observada se mantiene sobre otros cultivos y sobre otras etapas de desarrollo más avanzadas a la germinación y el crecimiento inicial

Does the Use of Tubular Digesters to Treat Livestock Waste Lower the Risk of Infection from \u3cem\u3eCryptosporidium Parvum and Giardia Lamblia\u3c/em\u3e?

Worldwide, high incidences of cryptosporidiosis and giardiasis are attributed to livestock waste. Quantitative microbial risk assessment can be used to estimate the risk of livestock related infections from Cryptosporidium parvum and Giardia lamblia. The objective of this paper was to assess the occupational and public health risks associated with management of raw and anaerobically digested livestock waste in two rural communities in Costa Rica based on fomite, soil and crop contamination and livestock waste management exposure pathways. Risks related to cattle waste were greater than swine waste due to cattle shedding more (oo)cysts. Cryptosporidium parvum also posed a greater risk than Giardia lamblia in all exposure pathways due to livestock shedding high loads of Cryptosporidium parvum oocysts and oocysts' lower inactivation rates during anaerobic digestion compared with Giardia lamblia cysts. The risk of infection from exposure to contaminated soil and crops was significantly lower for a community using tubular anaerobic digesters to treat livestock waste compared to a community where the untreated waste was applied to soil. The results indicate that treatment of livestock waste in small-scale tubular anaerobic digesters has the potential to significantly decrease the risk of infection below the World Health Organization's acceptable individual annual risk of infection (10−4).</jats:p