Full scale composting of food waste and tree pruning: How large is the variation on the compost nutrients over time?

The aim of the study was to evaluate if a composting unit on a commercial scale can produce, during 15 months, an organic compost according to the guarantees and tolerance margins required by Brazilian legislation for its nutrient content. For this, a food and tree pruning waste compost produced in a composting unit located in Belo Horizonte (Brazil) was evaluated. Noncompliance regarding tolerance margins for nitrogen, phosphorus and potassium were 3, 17 and 28% on a dry matter basis and 19, 31 and 33% on a fresh matter basis. Noncompliance can be mainly attributed to difference in the initial condition among piles (mass used in the piles preparation, proportion of food and pruning waste, initial nutrient content in the mixture, etc.) and differences in the operational activities among the piles. Together, these factors explained 64 to 86% of the variation in the nutrient content of the compost.

Representatividade da amostragem com emprego do trier na caracterização de leiras de compostagem de resíduos sólidos urbanos com base na Teoria da Amostragem de Pierre Gy / Sampling representativeness using trier in characterizing composting windrows of solid urban waste based on Pierre Gy's Sampling Theory

RESUMO O objetivo deste trabalho foi avaliar o desempenho do amostrador trier (NBR 10007/2004) na representatividade das propriedades de leiras de compostagem confeccionadas com resíduos sólidos urbanos, no início da degradação dos resíduos (8 dias) e no composto orgânico pronto (120 dias), utilizando como referência um método adaptado à compostagem a partir da Teoria da Amostragem de materiais heterogêneos. A compostagem foi conduzida em sistema de leiras revolvidas, e cada unidade contou com aproximadamente 30 toneladas de resíduos. O método do trier mostrou-se adequado para a caracterização do composto (120 dias), pois não apresentou diferenças significativas em relação ao método de referência na estimativa dos teores de matéria orgânica, nitrogênio, fósforo e potássio. Além disso, o revolvimento da leira antes da amostragem tem potencial para melhorar a representatividade do teor de água e do pH. Por outro lado, o amostrador trier mostrou-se limitado na amostragem de leiras em estágio inicial de compostagem, quando empregados resíduos com acentuada diferença de forma, tamanho e conteúdo de água das partículas. Embora reduza em menor magnitude os erros intrínsecos ao processo de amostragem, o método do trier é mais simples de ser conduzido e não demanda mecanização, espaço físico ou recursos humanos adicionais.

ABSTRACT This study was performed to assess the trier sampler performance (NBR 10007/2004) in representing the properties of windrows composting built with urban solid waste. It was evaluated in the beginning (8 days) and in the end of the composting process (120 days), using as a reference the Pierre Gy's Sampling Theory for heterogeneous materials. Composting windrows were built of 30 tons and carried out in turned windrow system. We found the trier method appropriate for characterizing mature compost (120 days) because it was similar to the reference method in estimating organic matter content, nitrogen, phosphorus and potassium. Besides, turning windrow before sampling might improve the representativeness of water content and pH. In contrast, more heterogeneous particles (shape, size, water content) may have influenced the trier's performance at the beginning of waste degradation and consequently the sample's accuracy. Although trier method is less efficient to reduce sampling errors than the method based on Sampling Theory, the former is simpler and does not need mechanization, extra space or additional human resources.

Addition of cattle manure to sheep bedding allows vermicomposting process and improves vermicompost quality.

Animal waste is usually a good substrate for vermicomposting. However, numerous animal husbandry systems use bedding that consists primarily of lignocellulosic substrates, which hinders earthworm and microorganism's development and thus, the entire bioconversion process. One possible solution is to mix the used bedding with other waste materials that are more amenable to earthworm ingestion and can provide better conditions for earthworm population growth. Here, we have aimed to examine the effectiveness of such procedure by mixing rice-husk-based sheep bedding with cattle manure in different proportions (0%, 25%, 50%, 75% and 100%). We have carried out vermicomposting experiments in benchtop vermireactors inoculated with 0.88kg of dry matter (sheep bedding+cattle manure). Data used in the Principal Component Analysis were the multiple vermicomposting variables (i.e., EC; pH; HA/FA and C/N ratios; P, K, cellulose, and hemicellulose content). The effect of the treatment on earthworm count was analyzed with ANOVA. We have observed that the addition of at least 25% of cattle manure to sheep bedding allows vermicomposting process but it is necessary 148days to obtain a stabilized vermicompost. However, increasing the proportion of cattle manure to sheep bedding, the vermicomposting time decreases proportionally to 94days. We concluded that vermicomposting can be considered a bioprocess to stabilize rice husk after being used as sheep bedding.

Performance of four stabilization bioprocesses of beef cattle feedlot manure.

The biological stabilization of beef cattle manure is crucial for promoting sanitation in feedlot pens. This study compared the performance of composting, vermicomposting, static windrows, and anaerobic digestion for stabilization of beef cattle feedlot manure based on the degradation of organic matter, nutrient retention, and stability of the final product in each process using uni- and multivariate analysis. The cluster analysis showed that composting and vermicomposting were the most similar processes. The principal component analysis showed that the more oxidative processes (composting and vermicomposting) degraded beef cattle feedlot manure more effectively (up to 45%) than static windrows and anaerobic digestion. Stabilization processes did not affect the amount of phosphorus, whereas potassium losses ranged from 3% (anaerobic digestion) to 30% (static windrow) and differed significantly across processes. Electrical conductivity decreased only in static windrow (30%). A decrease in the C/N ratio were observed in all processes, but the reduction was smaller in static windrow (5%). Larger reductions in C/N ratio were associated with greater increases in the humic to fulvic acid ratio. Composting and vermicomposting processes more effectively degraded beef cattle manure and produced stable organic fertilizers. Anaerobic digestion more effectively retained macronutrients (N and K) and converted organic N to ammonium. The use of static windrows is the least effective bioprocess for the stabilization of beef cattle feedlot manure.

The anaerobic co-digestion of sheep bedding and ⩾ 50% cattle manure increases biogas production and improves biofertilizer quality.

Sheep manure pellets are peculiarly shaped as small 'capsules' of limited permeability and thus are difficult to degrade. Fragmentation of manure pellets into a homogeneous mass is important for decomposition by microorganisms, and occurs naturally by physical shearing due to animal trampling, when sheep bedding is used. However, the high lignocellulose content of sheep bedding may limit decomposition of sheep manure. Here, we evaluated if co-digestion of sheep bedding with cattle manure would improve the yield and quality of the useful products of anaerobic digestion of sheep bedding--biogas and biofertilizer--by providing a source of nutrients and readily available carbon. Mixtures of sheep bedding and cattle manure in varying proportions (0%, 25%, 50%, 75%, or 100% cattle manure) were added to 6-L digesters, used in a batch system, and analyzed by uni and multivariate statistical tools. PC1, which explained 64.96% of data variability, can be referred to as 'organic fraction/productivity', because higher rates of organic fraction consumption (COD, cellulose and hemicellulose contents) led to higher digester productivity (biogas production, nutrient concentration, and sample stability changes). Therefore, productivity and organic fraction variables were most influenced by manure mixtures with higher (⩾ 50%) or lower (⩽ 25%) ratios of cattle manure, respectively. Increasing the amount of cattle manure up to 50% enhanced the biogas potential production from 142 L kg(-1)TS (0% of cattle manure) to 165, 171, 160 L biogas kg(-1)TS for the mixtures containing 100%, 75% and 50% of cattle manure, respectively. Our results show that the addition of ⩾ 50% cattle manure to the mixture increases biogas production and improves the quality of the final biofertilizer.