Abstract
This paper intended to explore the effect of alkaline H2O2 pretreatment on the biodegradability and the methane generation potential of greenhouse crop waste. A multi-variable experimental design was implemented. In this approach, initial solid content (3–7%), reaction time (6–24 h), H2O2 concentration (1–3%), and reaction temperature (50–100 °C) were varied in different combinations to determine the impact of alkaline H2O2 pretreatment. The results indicated that the alkaline H2O2 pretreatment induced a significant increase in the range of 200–800% in chemical oxygen demand (COD) leakage into the soluble phase, and boosted the methane generation potential from 174 mLCH4/g of volatile solid (VS) to a much higher bracket of 250–350 mLCH4/gVS. Similarly, the lignocellulosic structure of the material was broken down and hydrolyzed by H2O2 dosing, which increased the rate of volatile matter utilization from 31% to 50–70% depending on selected conditions. Alkaline H2O2 pretreatment was optimized to determine optimal conditions for the enhancement of methane generation assuming a cost-driven approach. Optimal alkaline H2O2 pretreatment conditions were found as a reaction temperature of 50 °C, 7% initial solid content, 1% H2O2 concentration, and a reaction time of six h. Under these conditions, the biochemical methane potential (BMP) test yielded as 309 mLCH4/gVS. The enhancement of methane production was calculated as 77.6% compared to raw greenhouse crop wastes.
Highlights
In the last few decades, there was a drastic change in the conceptual understanding of waste management
The cellulose, hemicellulose, lignin, and soluble matter contents of the fresh greenhouse crop waste were measured as 19.49%, 3.89%, 0.03%, and 76.58%, respectively
Crop waste was supplied by the growers, and fresh waste was sliced into approximately 1cm pieces, and was stored in sealed plastic bags at −20 ◦ C until used for composition analyses, alkaline H2 O2 pretreatment experiments, and methane generation potential tests
Summary
In the last few decades, there was a drastic change in the conceptual understanding of waste management. Waste is no longer considered as matter to be disposed of at the expense of additional cost, but as a resource. Energy recovery from waste is a hot topic, both in terms of scientific efforts and practical applications. Renewable energy sources, such as solar energy, wind energy, and geothermal energy, are being largely explored and exploited. Among these categories, biomass energy should be given specific emphasis mainly due to its accessibility; the energy recovery from biomass is quite sustainable as the proper disposal of biomass requires costly technical processes. Agricultural waste is Molecules 2018, 23, 1794; doi:10.3390/molecules23071794 www.mdpi.com/journal/molecules
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