Abstract
Biosolids are waste from wastewater treatment and have a high content of organic matter and nutrients. In this study, not conventional physicochemical and biological properties of biosolids produced during different seasons of the year were evaluated. These properties are not considered in environmental regulations; however, they are of agronomic interest as indicators of quality and functionality in soils. Also, molecular analysis by Fourier-transform infrared (FTIR) was conducted, enzymatic analysis using the APIZYM® system was performed and two indices of functional and microbial diversity were established. The results showed that the biosolids had a high content of total organic carbon, total nitrogen, P, and K. FTIR analyses showed that chemical composition of biosolids was similar during all year. The C and N of microbial biomass demonstrated presence of active microorganisms, as well as a uniformity in its richness and abundance of species that could present a positive synergy with soil microorganisms. The enzymatic activities showed that the biosolids contained an enzymatic machinery available to promote the mineralisation of the organic matter of biosolids and could even transcend into the soil. Finally, biological properties can be used as indicators of quality and functionality of biosolids before being used as an organic amendment, especially in agricultural soils.
Highlights
Waste sludge is a waste product that originated in the wastewater treatment process
In which biosolids have been generated from urban wastewater treatment and used for organic amendments, pH values have been reported in a range of 5.5 to 6.5 [13,63], similar to those obtained in this study
Analysis, it was concluded that biosolids can provide molecules, functional groups or chemically similar compounds, independent of the time in which these biosolids are generated, minimising the problem of their variability, which is a problem presented if they are used as an organic amendment to soils in the short- and long-term
Summary
Waste sludge is a waste product that originated in the wastewater treatment process. Wastewater treatment consists of a series of physical, chemical, and biological processes that have the purpose of eliminating the contaminants present in the water [1,2]. The second stage of wastewater treatment aims to eliminate dissolved organic matter present in wastewater [1,2,3] This stage is carried out mainly through processes of a biological nature that have in common the use of microorganisms to remove biodegradable organic matter [4]. The sludge generated in the secondary and tertiary stages of wastewater treatment is combined and sent to stabilisation processes [5]. These sludges are known as residual sludges and are characterized by a high content of degradable organic matter and nutrients, which can be used as soil improvers and even fertilizers for crops. The sludge is subjected to stabilisation processes to eliminate contaminants
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