RESUMEN
AIM: This study investigates differences in bacterial growth response in broth amended with compost-substrate extracts periodically bypassed during broiler litter composting. METHODS AND RESULTS: Compost samples, suspended in diluent were mixed with double strength broth into which ampicillin selective (0.3 g l(-1)) Escherichia coli and E. faecalis were separately seeded. Growth was measured by viable cell count. The Levenberg-Marquardt algorithm was applied to obtain a four-parameter sigmoidal function that best described the diminishing height transitions of the curves for extracts of increasing composting age. The time course of the growth rate followed a unimodal bell-shaped curve. The Microfit application was run to generate information of direct microbiological interest: increasing lambda and decreasing mu(max) for both bacteria with time. CONCLUSION: More than the curve-fitting process, the Unified model option of the Microfit application has confirmed the significant differences (P < 0.05) in the growth curve behaviour with more stabilized substrate extracts. The study demonstrates further scopes for characterization of the sanitization potential and indirectly, the impact of indigenous microbial competitive exclusion effects on enteric bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: A different outlook to understanding faecal bacterial growth dynamics in compost has been presented, using predictive microbiology concepts. Further structured studies are needed to fine-tune the generality of the findings for model development.
Asunto(s)
Enterococcus faecalis/crecimiento & desarrollo , Escherichia coli/crecimiento & desarrollo , Suelo , Algoritmos , Animales , Biodegradación Ambiental , Pollos , Recuento de Colonia Microbiana/métodos , Heces/microbiología , Matemática , Viabilidad Microbiana , Modelos BiológicosRESUMEN
An assessment of the effect of the composting potential of Mater-Bi biodegradable plastic with green wastes, noted by GBIO, and degradable plastic (PDQ-H additive) with green wastes, noted by GDEG, was carried out in a lagged two-compartment compost reactor. The composting time was determined until constant mass of the composting substrates was reached. The green wastes composting process was used as control (G). After one week of composting, the biodegradable plastics disappeared completely, while 2% of the original degradable plastic still remained after about 8 weeks of composting. A net reduction in volatile solids contents of 61.8%, 56.5% and 53.2% were obtained for G, GBIO and GDEG, respectively. Compost quality was assessed in terms of nitrogen, potassium and phosphorus contents, which were found to be highest for GBIO compost. From the phytotoxicity test, it has been observed that a diluted extract of GBIO compost has produced the longest length of radicle. From the respiration test, no significant difference in the amount of carbon dioxide released by the composting of GDEG and G was observed. This study showed that the quality of the compost is not affected by the presence of the biodegradable and degradable plastics in the raw materials.
Asunto(s)
Plásticos/metabolismo , Suelo , Plásticos/químicaRESUMEN
A study was conducted on two types of plastic materials, Mater-Bi Novamont (MB) and Environmental Product Inc. (EPI), to assess their biodegradability under aerobic and anaerobic conditions. For aerobic conditions, organic fractions of municipal solid wastes were composted. For the anaerobic process, anaerobic inoculum from a wastewater treatment plant was used. Cellulose filter papers (CFP) were used as a positive control for both mediums. The composting process was monitored in terms of temperature, moisture and volatile solids and the biodegradation of the samples were monitored in terms of mass loss. Monitoring results showed a biodegradation of 27.1% on a dry basis for MB plastic within a period of 72 days of composting. Biodegradability under an anaerobic environment was monitored in terms of biogas production. A cumulative methane gas production of 245 ml was obtained for MB, which showed good degradation as compared to CFP (246.8 ml). However, EPI plastic showed a cumulative methane value of 7.6 ml for a period of 32 days, which was close to the blank (4.0 ml). The EPI plastic did not biodegrade under either condition. The cumulative carbon dioxide evolution after 32 days was as follows: CFP 4.406 cm3, MB 2.198 cm3 and EPI 1.328 cm3. The cumulative level of CO2 varying with time fitted sigmoid type curves with R2 values of 0.996, 0.996 and 0.995 for CFP, MB and EPI, respectively.
Asunto(s)
Biodegradación Ambiental , Plásticos , Eliminación de Residuos/métodos , Aerobiosis , Anaerobiosis , Factores de TiempoRESUMEN
AIMS: The objective of this study was to deduce and analyse equations that best describe the behaviour of faecal bacterial indicators and two decomposition parameters during broiler litter composting. Mathematical models were fitted and the order of rate equations were identified. METHODS AND RESULTS: The Levenburg-Marquardt algorithm was used to fit nonlinear mathematical models to total coliforms (TC), faecal coliforms (FC), Escherichia coli (EC), faecal enterococci (FE), organic-C and volatile solids reduction, VS Red, by the least squares procedure. The rate equations showed that TC, FC and EC reductions were expressed by second-order decay kinetics. FE reduction followed first-order decay. Temperature dependency of decomposition rate was effectively verified by applying empirically derived rate equations. CONCLUSIONS: The governing mathematical models critically compare the inactivation kinetics of faecal indicators. TC, FC and EC were rapidly destroyed while FE was more resistant. Temperature elevation, organic-C and VS Red dynamics provide an accurate understanding of composting-induced decomposition of the broiler litter. SIGNIFICANCE AND IMPACT OF THE STUDY: The conservative performance of FE with respect to the other indicators has been established. Hence, FE presents better opportunities to encompass the totality of the composting process in terms of attainment of hygiene efficacy compared with EC.
Asunto(s)
Fenómenos Fisiológicos Bacterianos , Heces/microbiología , Microbiología del Suelo , Suelo , Algoritmos , Animales , Biodegradación Ambiental , Pollos , Enterococcus/fisiología , Escherichia coli/fisiología , Cocos Grampositivos/fisiología , Viabilidad Microbiana , Modelos Biológicos , TemperaturaRESUMEN
With the advent of recently promulgated Government regulations on plastics in Mauritius, a study was initiated to examine the biodegradability of two different types of plastic, namely Willow Ridge Plastics - PDQ-H additive (Plastic A) and Ecosafe Plastic - TDPA additive (Plastic B) under controlled and natural composting environments. The results obtained from the controlled composting environment showed that the cumulative carbon dioxide evolution for Plastic A was much higher than that for Plastic B. Plastic A therefore showed a higher level of biodegradation in terms of CO2 evolution than Plastic B. However, from the regression analysis, it was found that the level of CO2 varying with time fitted the sigmoid type curves with very high correlation coefficients (R2 values: 0.9928, 0.9921 and 0.9816, for reference material, inoculum and Plastic A, respectively). The corresponding F-values obtained from the ANOVA analysis together with significance levels of p<0.05 indicated that the three treatments analysed in the biodegradability experiment were significant. The other experiment was undertaken to observe any physical change of Plastics A and B as compared to a reference plastic, namely, compostable plastic bag (Mater-Bi product-Plastic C), when exposed to a natural composting environment. Thermophilic temperatures were obtained for about 3-5 days of composting and the moisture content was in the range of 60-80% throughout the degradation process. It was observed that after 55 days of composting, Plastic C degraded completely while Plastic A and Plastic B did not undergo any significant degradation. It can be concluded that naturally based plastic made of starch would degrade completely in a time frame of 60 days, whereas plastics with biodegradable additive would require a longer time.
Asunto(s)
Ambiente , Plásticos/metabolismo , Suelo , Aerobiosis , Biodegradación Ambiental , Dióxido de Carbono , Compuestos Orgánicos/metabolismo , Estándares de Referencia , Análisis de Regresión , Temperatura , Factores de TiempoRESUMEN
This study was initiated to characterize solid and liquid wastes generated in healthcare institutions and to provide a framework for the safe management of these wastes. The project was carried at three major medical institutions, namely, the Jeetoo Hospital, the Sir Seewoosagur Ramgoolam National (SSRN) Hospital and the Clinic Mauricienne. A waste audit carried out at these sites revealed that approximately 10% of solid wastes was hazardous in nature, consisting mainly of infectious, pathological and chemical wastes. The average amount of hazardous wastes per patient per day was found to be 0.072 kg at Jeetoo hospital, 0.091 kg at SSRN hospital and 0.179 kg at the clinic. The amount of hazardous wastes generated as a function of the number of occupied beds was found to follow a relationship of type y=0.0006x-0.19, where y was the amount of hazardous wastes generated per bed per day and x was the number of occupied beds. The waste quantifying process also revealed that at SSRN Hospital, 0.654 m(3) of water was being consumed per patient per day and the amount of wastewater produced was 500 m(3)/day. Further analysis revealed that the wastewater was polluting with chemical oxygen demand (COD), biological oxygen demand (BOD(5)), total suspended solids (TSS) and coliform content well above permissible limits.