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Phosphorus recovery from waste streams stands out as a strategic practice to ensure phosphorus availability to future generations. The release of phosphate mediated by biological sulfate reduction is an interesting bioprocess for phosphorus recovery from sewage sludge in wastewater treatment plants in which chemical phosphorus recovery is foreseen. This study investigates the effect of biological sulfate reduction at different feed sulfate concentrations (up to 8000 mg L−1) on the anaerobic phosphate release from both sewage sludge and digestate as well as the impact of sulfate addition on energy recovery from the sludge viabiomethane production. During anaerobic digestion, up to 62.3% of the phosphate initially present in the sludge as iron(iii) phosphate was released with 8000 mg L−1feed sulfate. However, biomethane production was significantly reduced (>40%) when sulfate was added at concentrations above 100 mg L−1. The use of thermal hydrolysis on the sludge digestate was found to be an effective strategy for phosphorus recovery from the sludge without compromising the biomethane production during anaerobic digestion. A phosphate release from iron(iii) phosphate of up to 48.7% was obtained when adding 4000 mg L−1sulfate to the digestate previously hydrolyzed for 2 hours. Finally, the implementation potential of the proposed strategy in full-scale wastewater treatment plants is discussed.

The efficient management of municipal sewage sludge (MSS) daily produced worldwide by biological wastewater treatment processes is nowadays of utmost importance. Classic treatment/disposal methods are affected by efficiency and/or safety issues. Innovative thermochemical treatments are gaining momentum as promising alternatives. Pyrolysis of MSS can result in the recovery of precious resources, such as nutrients and organic matter, and their conversion into three valuable fractions, i.e.biochar, bio-oil, and pyrolysis gas. These products are employable in innovative biorefinery pathways towards a wide range of value-added materials. In this review, an integrated biorefinery platform for MSS valorization is presented. After a brief introduction on MSS properties and issues related to its management, a deep focus on the influence that the feedstock and pyrolysis conditions have on the product yields and composition was conducted. Innovative valorization routes for biochar, bio-oil and pyrolysis gas were extensively discussed by highlighting challenges, opportunities, advantages and drawbacks. The characteristics required by these products to be efficiently valorized, as well as the main solution for their enhancement, were described. Additionally, economic considerations on MSS pyrolysis derived from full-scale applications conducted at the European and global level were elaborated. Finally, future perspectives about biochar, bio-oil and pyrolysis gas employment in cutting-edge upcycling routes have been reported.

Nitrate (NO3-) pollution in aquatic environments, mainly due to the excessive use of nitrogen-based fertilizers and chemicals, poses significant risks to water quality and human health. Bioelectrochemical systems (BESs) have emerged as innovative solutions to complement traditional wastewater treatment methods for effective NO3-removal, addressing the need for sustainable approaches to wastewater management at different scales. In this study, the NO3-removal potential of a denitrifying double-chamber flow-through BES applied as post-treatment of an aerobic granular sludge system used for combined carbon and nitrogen removal was evaluated for 63 days under different feed (anodic and cathodic) and hydraulic retention time (HRT) (2–10 h) conditions. After 6 days of biomass acclimatization and at an HRT of 2 h, complete removal of N-NO3−and N-NO2−was achieved primarily through heterotrophic denitrification due to the presence of acetate. Nevertheless, using only the electrode as the electron source resulted in NOx(NO3−+ NO2−) removal efficiencies of up to 65 ± 16 %, with NOxconcentrations remaining below the Italian standard for industrial effluent discharge into sewers (30 mg N-NO3−·L−1and 0.6 mg N-NO2−·L−1), demonstrating the good performance and applicability of the system even in the absence of organic carbon in the feed. The combined autotrophic and heterotrophic denitrification resulted in lower specific energy consumption compared to the use of autotrophic denitrification alone, ranging from 2.3·10−2to 9.6·10−5kWh·g NOx, removed−1at an HRT of 2 h.

Thespreading of nitrogenous compounds into the environment is a common challenge duringmining industries. Typical explosives used in mining are N-based compoundswhich lead to nitrogen contamination of groundwater and water bodies. In goldextraction, cyanide used as lixiviant is also another source of nitrogen pollution.The present work aims to investigate the effect of heavy metals ondenitrification using batch bioassays. Cu, Ni, Co and Fe influence ondenitrification process was studied at pH 7.0. Below the soluble concentrationof 62 mg/L, Ni did not inhibit denitrification, whereas denitrification wasrepressed at soluble Ni concentration above 62 mg/L. At 122 mg/L of soluble Ni,50% inhibition of denitrification was observed. Below soluble concentration of86 mg/L, Co exerted no inhibitory effect on nitrate removal but moderatelydecreased the denitrification rate. Cu slowed denitrification down resulting in40% of nitrate removal averagely at the soluble concentration below 1 mg/L. Onthe contrary, Fe supplementationresulted in iron oxidation and soluble Fe concentrations ranging from 0.4-1.6mg/L that stimulated denitrification. Thepresent work indicates that denitrification can tolerate heavy metals and canbe suitable for acid mine drainage remediation.

This study is prompted by the high leaching efficiency of Zijinshan copper bio-heap leaching industrial plant. Bioleaching columns with 100 mm diameter and 1 m height were used to investigate copper bioleaching at different operating conditions. Elevated temperature, high total iron concentration and high acidity significantly increased copper leaching rate as determined by solution and residue assays. At 60 oC with 50 g/L iron (initial Fe3+/Fe2+ gram ratio 2.5), pH 1.0 and no aeration, copper extraction was achieved 90% after 60 days. However, at 30oC, 5 g/L total Fe, pH 1.5 and no aeration, copper extraction reached 80% and 85% after 90 and 200 days, respectively. Real-time PCR assay showed that only 105 cells/ml and 2×105 cells/g are in solution and on the ore surface at the condition of 60 oC 50 g/L iron and pH 1.0, respectively. In addition, a similar leaching rate was observed in the tests with and without inoculation. The column without inoculation was directly irrigated with acid mine drainage (AMD). Our results indicate high copper leaching efficiency at extreme conditions for mineral oxidizing bacteria. Inoculation and aeration are not necessary in Zijinshan copper mine bio-heap leaching process.

PAHs are largely spread in the aquatic environment, and the drawbacks of conventional remediation techniques as well as the expenditures for alternative disposal of polluted sediments lead to seek more effective, environmentally–friendly and sustainable approaches. Therefore, the present review shows a critical overview of the literature evaluated with VOSviewer, focusing on the problem of PAH–contaminated marine sediments and the knowledge of available remediation processes to shed light on what research and technology lack. This review supplies specific information about the key factors affecting biological, physical–chemical and thermal remediation techniques, and carefully examines the drawbacks associated with their employment for remediating PAH–polluted marine sediments by showing adequate alternatives. The technologies thoroughly discussed here are biostimulation, bioaugmentation, sediment washing, carbonaceous adsorbent addition and thermal desorption. The environmental and economic impacts associated with the application of the mentioned remediation technologies have been also taken into account. Finally, this review examines new research directions by showing future recommendations.