Academic journal article Journal of Environmental Engineering and Science

Composting of Municipal Biosolids: Effect of Bulking Agent Particle Size on Operating Performance (1)

Academic journal article Journal of Environmental Engineering and Science

Composting of Municipal Biosolids: Effect of Bulking Agent Particle Size on Operating Performance (1)

Article excerpt

Abstract: Woodchips, prepared from wood waste obtained from a pallet manufacturer, were used to determine the effect of bulking agent particle size on compost pile performance. The three treatments investigated used coarse, medium, or fine woodchips. Characteristic particle sizes were 40, 13, and 5.2 mm for the coarse, medium, and fine material, respectively. All recipes were made using one part biosolids to 2.5 parts woodchips (v:v) at a target moisture content of 60%. Finer woodchips resulted in thermophilic temperature values being reached sooner, being sustained for a longer time (>95 d), and recovering more quickly after rainfall events. Finer woodchips also resulted in lower moisture loss over the experimental period. Based on the experimental observations, it was assumed decreased tortuosity in the coarse woodchip material led to higher ventilation rates as compared to the finer material. Further experimental work is required to confirm this. The authors' recommend operators characterize feedstock bulking agent particle size distribution, particularly at facilities purchasing bulking agents for their operations.

Key words: compost, municipal biosolids, woodchips, particle size, bulking agent, temperature.

Resume : Des copeaux de bois prepares a partir de dechets de bois, provenant d'un fabricant de palettes, ont ete utilises pour determiner l'effet de la dimension des particules de l'agent gonflant sur le rendement de la halde de compost. Les trois traitements etudies utilisaient des copeaux grossiers, moyens et petits. Les dimensions typiques de particules etaient de 40, 13 et 5,2 mm respectivement pour les materiaux grossiers, moyens et petits. Toutes les recettes utilisaient une portion de biosolides pour 2,5 portions de copeaux (vol:vol) a une teneur en eau cible de 60 %. Des copeaux de bois plus fins ont fait que les temperatures thermophiles ont ete atteintes plus rapidement, etaient maintenues pendant longtemps (>95 jours) et recuperaient plus rapidement apres les pluies. Des copeaux de bois plus fins ont egalement engendre la plus faible perte d'humidite durant la periode d'etude. Selon les observations, l'hypothese a ete emise qu'une diminution du coefficient de tortuosite dans les copeaux grossiers engendrait des plus forts taux de ventilation que les materiaux plus fins. Des travaux experimentaux additionnels sont cependant requis pour le confirmer. Les auteurs recommandent que les operateurs caracterisent la distribution granulometrique de l'agent gonflant des charges d'alimentation, plus particulierement aux installations achetant des agents gonflants pour leurs operations.

Mots cles : compost, biosolides municipaux, copeaux de bois, dimension des particules, agent gonflant, temperature.

[Traduit par la Redaction]

Introduction

Recent studies examining the feasibility of composting biosolids through extremely cold winters (Eftoda and McCartney 2004), led to the belief that bulking agent particle size plays an instrumental role in compost pile temperatures. Haug (1980) suggested that as bulking agent particle size increases, natural ventilation through a static windrow increases as well. This leads to increased heat loss via convection and evaporation since the ambient air being drawn through the windrow is drier and cooler than the air inside the windrow. Numerous composting studies have been performed over the past 30 years, but few have examined the effects of the particle size of bulking agent used. Haug (1993) suggested woodchips from 25.4 to 50.8 mm (1 to 2 in.) in size are the most commonly used bulking agents, while woodchips ranging from 3.2 to 50.4 mm (1/8 to 2 in.) mean diameter have been shown to yield good results (Willson 1989; Francos et al. 1982). Higgins et al. (1986) tested three different textures of shredded rubber tires as bulking agents; (1) small (12.7 to 25.4 mm), medium (25.4 to 50.8 mm), and large (above 50.8 mm). They found that particles ranging from 12. …

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