Comprehensive quality assessment of municipal organic waste composts produced by different preparation methods.

In the first part of this work, the effect of municipal organic waste (MOW) composts on plant growth was evaluated in a greenhouse trial. The treatments included soil amended with 14 different composts (prepared by shredding, adding wood shavings, cocomposting with biosolids or vermicomposting), an inorganically fertilized soil, and a control soil. All of the treatments significantly increased plant growth compared to the control, and yields of three of the amended treatments were as high as that of the inorganic fertilizer treatment. When comparing differently prepared composts to the conventional compost, it was found that cocomposting MOW with biosolids was the method which most positively influenced yields (26-41% yield increases). In the second part of this work, we evaluated the effects of the different preparation methods on compost quality, using a multivariate approach. Three main quality aspects were considered collectively in a principal component analysis: organic matter and nutrient concentrations, degradability and capacity to mineralize these nutrients, and plant growth. The model was restricted to the first and second components (PC1 and PC1) which accounted for 94% of data variance. On the resulting factorial plane, four groups were distinguished. Each of the groups was compared to the reference compost to determine quality increases or decreases. Based on this analysis, it was found that cocomposting MOW with biosolids produced the highest quality products (higher total nutrient and OM concentration, nutrient mineralization potential, and plant growth). Addition of wood shavings increased OM concentration, but reduced quality in terms of the other aspects studied. Shredding was only effective to increase product quality when it was not combined with other methods, whereas vermicomposting only increased quality when MOW was not mixed with biosolids.

Co-composting rice hulls and/or sawdust with poultry manure in NE Argentina.

Rice hulls and sawdust are two common C-rich wastes derived from rice and timber agro-industries in subtropical NE Argentina. An alternative to the current management of these wastes (from bedding to uncontrolled burning) is composting. However, given their C-rich nature and high C/N ratio, adequate composting requires mixing with a N-rich waste, such as poultry manure. The effect of different proportions of poultry manure, rice hulls and/or sawdust on composting efficiency and final compost quality was studied. Five piles were prepared with a 2:1 and 1:1 ratio of sawdust or rice hulls to poultry manure, and 1:1:1 of all three materials (V/V). Different indicators of compost stability and quality were measured. Thermophilic phase was shorter for piles with rice hulls than for piles with sawdust (60 days vs. 105 days). Time required for stability was similar for both C-rich wastes (about 180 days). Characteristics of final composts were: pH 5.8-7.2, electrical conductivity 2.5-3.3 mS/cm, organic C 20-26%, total N 2.2-2.9%, lignin 19-22%, total Ca 18-24 g/kg, and extractable P 6-8 g/kg, the latter representing 60% of total P. Nitrogen conservation was high in all piles, especially in the one containing both C-rich wastes. Piles with sawdust were characterized by high total and available N, while piles with only rice hulls had higher Si, K and pH. Extractable P was higher in 1:1 piles, and organic C in 2:1 piles.

Improving the quality of municipal organic waste compost.

The effects of different municipal organic waste (MOW) management practices (shredding, addition of carbon-rich materials and inoculation with earthworms) on organic matter stabilization and compost quality were studied. Four static piles were prepared with: (i) shredded MOW; (ii) shredded MOW+woodshavings; (iii) non-shredded MOW; and (iv) non-shredded MOW+woodshavings. After 50 days, a part of each pile was separated for vermistabilization, while the rest continued as traditional thermophilic composting piles. At different sampling dates, and in the finished products, the following parameters were measured: pH, electrical conductivity, carbon dioxide evolution, and concentrations of organic matter, total nitrogen, water-soluble carbon, nitrate nitrogen, ammonium nitrogen, and extractable phosphorus. Shredded treatments exhibited faster organic matter stabilization than non-shredded treatments, evidenced specially by earlier stabilization of carbon dioxide production and shorter thermophilic phases. Woodshavings addition greatly increased quality of final products in terms of organic matter concentration, and pH and electrical conductivity values, but decreased total nitrogen and available nutrient concentrations. Vermicomposting of previously composted material led to products richer in organic matter, total nitrogen, and available nutrient concentrations than composting only, probably due to the coupled effect of earthworm activity and a shorter thermophilic phase.

Factors related to the attraction of flies at a biosolids composting facility (Bariloche, Argentina).

The composting process is used to treat biosolids from the Wastewater Treatment Plant of Bariloche (NW Patagonia, Argentina). Since 1998, an odourless, innocuous and stable organic amendment has been produced at the Biosolids Composting Plant of Bariloche. However, volatile compounds produced during this process, attract different vectors, mainly insects belonging to the Order Diptera, particularly in summer. To evaluate factors associated with the attraction of Diptera to composting windrows, volatile compounds, wind velocity, ambient and windrow temperatures were measured and their relationships with the taxa of flies found were determined. Sampling was conducted several months on newly formed windrows during 3 weeks of the thermophilic composting period. Composite samples from each windrow were taken on the first day of each sampling week, from November 1999 to March 2000 to analyze volatile compounds using an 'electronic nose'. Windrow and ambient temperatures and wind velocity were recorded on three consecutive days of each week, from January to March 2000; also the capture of flies was performed in this period. A weekly mean value was calculated for each environmental variable. Canonical Correspondence Analysis was employed to determine relationships between taxa of flies and the studied factors. The electronic nose discriminated among odours emitted, differentiating windrows by the bulking agent employed and by week of the thermophilic composting period. Ambient temperatures increased slightly during the sampling weeks; the highest values of wind velocity were registered during the second sampling week while windrow temperatures were sustained approximately 60 degrees C. Canonical Correspondence Analysis showed that attraction of flies to composting windrows was related to minimum and maximum ambient temperatures and volatile compounds for Muscina stabulans, Fannia sp. and Acaliptratae and to wind velocity for Ophyra sp., Sarcophaga sp., Cochliomyia macellaria and Phaenicia sericata.

Composting of fish offal and biosolids in northwestern Patagonia.

Composting of fish processing wastes and biosolids with wood by-products and yard trimmings was conducted during the summer of 1996 and winter of 1997 in NW Patagonia using: (i) static piles for fish offal and (ii) turning piles for biosolids. Fish offal was mixed with sawdust + wood shavings (FOC) at 3:1 ratio by weight and biosolids with wood shavings (BCw) and yard trimmings (BCt) at 1:1 ratio by volume. Samples were taken at six dates during the composting period and analyzed to determine the factors that predict compost maturity. Composting of biosolids was affected by the type of bulking agent during winter. Thermophilic temperatures > or = 55 degrees C were sustained long enough to satisfy the USEPA requirements for processes to further reduce pathogens (PFRP) in FOC and BCt, and for processes to significantly reduce pathogens (PSRP) in summer BCw, while in winter BCw temperatures were lower than those recommended for effective pathogen reduction. However, coliform fecal content in all BC treatments was less than 10 most probable number (MPN) g(-1) dry sample at the end of the process. The ratio of water soluble carbon (WSC) to total nitrogen (TN) appeared to be a more adequate index to predict compost maturity than the ratio of total organic carbon to nitrogen.

Compostaje como alternativa de manejo de biosolidos: la experiencia de Bariloche

Por pedido de la empresa responsable de la Planta de Saneamiento de Bariloche (SURBASA) y mientras finalizaba su construccion, el Grupo de Suelos del CRUB inicio estudios de compostaje de biosolidos en 1995. Estas experiencias se realizaron en base a lodos provenientes de plantas de tratamiento de la region. En 1997 SURBASA construyo la Planta de Compostaje de Lodos de la Ciudad de Bariloche, la primera del pais con controles segun exigencias de organismos internacionales. La experiencia constituye un ejemplo de la posible colaboracion entre empresas privadas e instituciones publicas

Lodos cloacales en Bariloche: de residuos peligrosos a recurso agronómico

Se presenta este trabajo, donde se han utilizado materiales cloacales provenientes de distintas plantas de tratamiento de liquidos cloacales de Bariloche. Los estudios incluyen -analisis del contenido de nutrientes, de elementos pesados y de patogenos, -estudios de laboratorio e invernáculo, -estrategias de manejo. Los resultados preliminares obtenidos en base estas experiencias han permitido la elaboracion de un plan de manejo de lodos de la ciudad en un emprendimiento en comun entre SURBASA S.A. y un empresario local, que actualmente se encuentra en fase de evaluacion del impacto ambiental en la Municipalidad de S.C. de Bariloche

Lodos cloacales en Bariloche: de residuos peligrosos a recurso agronómico

Se presenta este trabajo, donde se han utilizado materiales cloacales provenientes de distintas plantas de tratamiento de liquidos cloacales de Bariloche. Los estudios incluyen -analisis del contenido de nutrientes, de elementos pesados y de patogenos, -estudios de laboratorio e invernáculo, -estrategias de manejo. Los resultados preliminares obtenidos en base estas experiencias han permitido la elaboracion de un plan de manejo de lodos de la ciudad en un emprendimiento en comun entre SURBASA S.A. y un empresario local, que actualmente se encuentra en fase de evaluacion del impacto ambiental en la Municipalidad de S.C. de Bariloche