Abstract
The composting of sewage sludge and maize straw mixtures was investigated in this study. The aim was to analyze the influence of different proportions of sewage sludge and maize straw in the mixtures on composting process dynamics (expressed by heat production) and gas emissions. The results showed that all examined mixtures reached a strong thermophilic phase of composting; however, the lowest dynamic of temperature growth was observed in the case of the biggest sewage sludge content (60% of sewage sludge in the composting mixture). The ammonia concentration inside bioreactor chambers was directly related to the content of sewage sludge in the composted mixture. Excessive contents of sewage sludge had a considerable effect on very low C/N ratios and high losses through ammonia emissions. Tests were carried out in reactors with a capacity of 160 dm3 under controlled conditions. All mixtures were aerated by the average air-flow of about 2.5 dm3∙min−1, i.e., the minimum air-flow that allows a temperature of about 70 °C to be reached and a sufficiently long thermophilic phase, which ensures proper composting.
Highlights
The rapid development of urbanization and industrialization all over the world, including Europe, has significantly increased the amount of sewage [1,2,3]
The aim of this study was to analyze the influence of different proportions of sewage sludge and maize straw mixtures on composting process dynamics, heat energy, and gas emissions
Sewage sludge was mixed with maize straw in different proportions (Table 1), with the substrate weight and the percentage ratios expressed in terms of fresh mass (FM) and total solids (TS), respectively
Summary
The rapid development of urbanization and industrialization all over the world, including Europe, has significantly increased the amount of sewage [1,2,3]. Data specifying the current level of wastewater production and treatment has been of global importance for the last few years, and has been important for national decision makers, researchers, practitioners, and public institutions, in order to develop national policies and action plans for wastewater treatment and the productive use of it (in many sectors—from agriculture, to industry). Per capita production in individual countries varies greatly and depends mainly on the percentage of the population with households connected to collective sewerage systems It determines what type of sludge is included in the calculations—raw, treated, only domestic, etc. The following solids production rates may be used: 0.2–0.3 kg·m−3 of treated wastewater with an average rate of
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