Abstract
Conventional wastewater treatment generates large amounts of organic matter–rich sludge that requires adequate treatment to avoid public health and environmental problems. The mixture of wastewater sludge and some bulking agents produces a biosolid to be composted at adequate composting facilities. The composting process is chemically and microbiologically complex and requires an adequate aeration of the biosolid (e.g., with a turner machine) for proper maturation of the compost. Adequate (near) real-time monitoring of the compost maturity process is highly difficult and the operation of composting facilities is not as automatized as other industrial processes. Spectroscopic analysis of compost samples has been successfully employed for compost maturity assessment but the preparation of the solid compost samples is difficult and time-consuming. This manuscript presents a methodology based on a combination of a less time-consuming compost sample preparation and ultraviolet, visible and short-wave near-infrared spectroscopy. Spectroscopic measurements were performed with liquid compost extract instead of solid compost samples. Partial least square (PLS) models were developed to quantify chemical fractions commonly employed for compost maturity assessment. Effective regression models were obtained for total organic matter (residual predictive deviation—RPD = 2.68), humification ratio (RPD = 2.23), total exchangeable carbon (RPD = 2.07) and total organic carbon (RPD = 1.66) with a modular and cost-effective visible and near infrared (VNIR) spectroradiometer. This combination of a less time-consuming compost sample preparation with a versatile sensor system provides an easy-to-implement, efficient and cost-effective protocol for compost maturity assessment and near-real-time monitoring.
Highlights
IntroductionThe treatment of domestic and industrial wastewater is usually associated with the production of an organic matter–rich (and potentially dangerous due to the presence of pathogens, and even heavy metals and micropollutants) sludge [1,2]
The treatment of domestic and industrial wastewater is usually associated with the production of an organic matter–rich sludge [1,2]
We include an example of a characteristic absorbance UV spectrum obtained for samples located include an example of a characteristic absorbance UV spectrum obtained for samples located at the at thebeginning beginning of the composting process
Summary
The treatment of domestic and industrial wastewater is usually associated with the production of an organic matter–rich (and potentially dangerous due to the presence of pathogens, and even heavy metals and micropollutants) sludge [1,2]. The implementation of new environmental regulations is promoting an increase in the quantities of wastewater sewage sludge due to the constant rise in the number of households connected to sewers and the increase in the level of treatment. The production of sewage sludge in the European Union increased from 5.5 million tons of dry matter in 1992 [3] to more than 10 million tons in 2012 (data calculated from [4]). Options for sludge treatment include stabilization (e.g., composting, anaerobic digestion), thickening, dewatering, drying and incineration [5]
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