The link between organic matter composition and the biogas yield of full-scale sewage sludge anaerobic digestion

Adsorption of phosphate over a novel magnesium-loaded sludge-based biochar

The production of sludge-based biochar to recover phosphorus (P) from wastewater and reuse the recovered phosphorus as agricultural fertilizer is a preferred process. This article mainly studied the removal of phosphate (PO4-P) from aqueous solution by synthesizing sludge-based biochar (MgSBC-0.1) from anaerobic fermentation sludge treated with magnesium (Mg)-loading-modification, and compared it with unmodified sludge-based biochar (SBC). The physicochemical properties, adsorption efficiency, and adsorption mechanism of MgSBC-0.1 were studied. The results showed that the surface area of MgSBC-0.1 synthesized increased by 5.57 times. The material surface contained MgO, Mg(OH)2, and CaO nanoparticles. MgSBC-0.1 can effectively remove phosphate in the initial solution pH range of 3.00-7.00, with a fitted maximum phosphorus adsorption capacity of 379.52 mg·g-1. The adsorption conforms to the pseudo second-order kinetics model and Langmuir isotherm adsorption curve. The characterization of the adsorbed composite material revealed the contribution of phosphorus crystal deposition and electrostatic attraction to phosphorus absorption.

Do contaminants compromise the use of recycled nutrients in organic agriculture? A review and synthesis of current knowledge on contaminant concentrations, fate in the environment and risk assessment

Use of nutrients recycled from societal waste streams in agriculture is part of the circular economy, and in line with organic farming principles. Nevertheless, diverse contaminants in waste streams create doubts among organic farmers about potential risks for soil health. Here, we gather the current knowledge on contaminant levels in waste streams and recycled nutrient sources, and discuss associated risks. For potentially toxic elements (PTEs), the input of zinc (Zn) and copper (Cu) from mineral feed supplements remains of concern, while concentrations of PTEs in many waste streams have decreased substantially in Europe. The same applies to organic contaminants, although new chemical groups such as flame retardants are of emerging concern and globally contamination levels differ strongly. Compared to inorganic fertilizers, application of organic fertilizers derived from human or animal feces is associated with an increased risk for environmental dissemination of antibiotic resistance. The risk depends on the quality of the organic fertilizers, which varies between geographical regions, but farmland application of sewage sludge appears to be a safe practice as shown by some studies (e.g. from Sweden). Microplastic concentrations in agricultural soils show a wide spread and our understanding of its toxicity is limited, hampering a sound risk assessment. Methods for assessing public health risks for organic contaminants must include emerging contaminants and potential interactions of multiple compounds. Evidence from long-term field experiments suggests that soils may be more resilient and capable to degrade or stabilize pollutants than often assumed. In view of the need to source nutrients for expanding areas under organic farming, we discuss inputs originating from conventional farms vs. non-agricultural (i.e. societal) inputs. Closing nutrient cycles between agriculture and society is feasible in many cases, without being compromised by contaminants, and should be enhanced, aided by improved source control, waste treatment and sound risk assessments.

Synergistic lignin degradation between Phanerochaete chrysosporium and Fenton chemistry is mediated through iron cycling and ligninolytic enzyme induction

Removal of recalcitrant lignin from wastewater remains a critical bottleneck in multiple aspects relating to microbial carbon cycling ranging from incomplete treatment of biosolids during wastewater treatment to limited conversion of biomass feedstock to biofuels. Based on previous studies showing that the white rot fungus Phanerochaete chrysosporium and Fenton chemistry synergistically degrade lignin, we sought to determine optimum levels of Fenton addition and the mechanisms underlying this synergy. We tested the extent of degradation of lignin under different ratios of Fenton reagents and found that relatively low levels of H2O2 and Fe(II) enhanced fungal lignin degradation, achieving 80.4 ± 1.61 % lignin degradation at 1.5 mM H2O2 and 0.3 mM Fe(II). Using a combination of whole-transcriptome sequencing and iron speciation assays, we determined that at these concentrations, Fenton chemistry induced the upregulation of 80 differentially expressed genes in P. ch including several oxidative enzymes. This study underlines the importance of non-canonical, auxiliary lignin-degrading pathways in the synergy between white rot fungi and Fenton chemistry in lignin degradation. We also found that, relative to the abiotic control, P. ch. increases the availability of Fe(II) for the production of hydroxyl radicals in the Fenton reaction by recycling Fe(III) (p < 0.001), decreasing the Fe(II) inputs necessary for lignin degradation via the Fenton reaction.