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Swine slurry is generated in large quantities and anaerobic digestion may represent an appropriate process to both treat and revalue this waste as an energy source. Pretreatment processes aim to increase the anaerobic biodegradability of a specific waste. In this study, steam explosion and weak thermal-alkali pretreatments are evaluated. The first series of Biochemical potential (BMP) test is set to establish the best substrate/inoculum ratio conditions, and then other tests are carried out to assess the impact of these pretreatments on the methane potential and maximum production rate by using the modified Gompertz equation. The S/I ratio exerts an influence on the BMP results and the optimum ratio was found to be between 0.1–0.25 gVSs gVS I −1 . Steam explosion leads to an improvement of both the methane potential and the maximum production rate at the highest severity conditions. Weak alkali thermal pretreatment improved the maximum production rate but affected negatively the methane potential of the substrate. [ABSTRACT FROM AUTHOR]

• Alkaline pretreatment was the most effective in lignin removal of olive pomace. • Alkaline pretreatment increased methane produced by 30%. • Lipid contents in alkali and ultrasonic pretreated solids were highly reduced. • Single microwave and ultrasound were less effective than combined pretreatments. This study aims to investigate the effects of microwaves, ultrasonic and alkaline pretreatments on olive pomace properties and its biomethane potential. Alkaline pretreatment was found to reduce lipid and fiber contents (especially lignin) and to increase soluble matter. The alkali pretreatment at a dose of 8% (w/w TS) under 25 °C and for 1 day removed 96% of initial lipids from the solid olive pomace. Unlike NaOH addition, mild microwaves and ultrasonic pretreatments had no impact on lignin. However, in the case of long microwaves pretreatment (450 W-10 min), cellulose and lignin contents were reduced by 50% and 26% respectively. Similarly, the combination of ultrasonic and alkali reagent showed a positive effect on fiber degradation and lipid solubilization as well as a positive impact on methane production. Statistical analysis highlighted the correlation between NaOH dose, solubilization and methane production. The alkaline pretreatment at ambient temperature appeared the most energetically efficient. [ABSTRACT FROM AUTHOR]

• Valorization of macroalgal residues by anaerobic digestion. • Knife milling and alkaline pretreatment enhanced methane production. • In semi-continuous reactors, alkaline pretreatment enhanced methane by 20%. • Digestates did not exhibit phytotoxicity. • Digestate from codigestion with sludge led to the highest tomato plant growth. The aim of this paper is to investigate the impact of pretreating macroalgal residue (MAR) from agar-agar extraction and its co-digestion with sewage sludge on methane production and the agronomic quality of the digestates produced. First, different pretreatments were assessed on BMP tests. Among milling technologies used, knife milling with a 4 mm-screen improved methane production by 25%. The MAR was then knife milled before alkaline, acid and thermal pretreatment. KOH pretreatment (5% TS basis, 25 °C for 2 days) led to the highest methane improvement. It was applied to semi-continuous anaerobic digestion and methane production achieved 237 Nml/gVS which was 20% higher than the control (198 Nml/gVS). In comparison to MAR mono-digestion, co-digestion with thickened activated sludge produced less methane (184 Nml/gVS) but reduced H 2 S emission by 91%. None of the digestates was toxic for the germination or growth of wheat and tomato plants. Particularly, co-digestion had the highest impact on tomato plant dry weight (+94% compared to soil alone) mainly due to the phosphorous brought by sludge. However, the impact of alkaline pretreatment on plant growth was not significant. [ABSTRACT FROM AUTHOR]

This study aims at investigating how organic waste co-digestion coupled with alkaline pretreatment can impact the methane production and agronomic value of produced digestates. For this purpose, sludge alone and mixed with olive pomace or macroalgal residues were subjected to anaerobic digestion with and without alkaline pretreatment. In addition, co-digestion of pretreated sludge with raw substrates was also carried out and compared to the whole mixture pretreatment. KOH pretreatment enhanced methane production by 39%, 15% and 49% from sludge, sludge mixed with olive pomace and sludge mixed with macroalgal residues, respectively. The digestates were characterised according to their physico-chemical and agronomic properties. They were then applied as biofertilizers for tomato growth during the first vegetative stage (28 days of culture). Concentrations in chlorophyll a and carotenoids in tomato plants, following sludge digestate addition, rose by 46% and 41% respectively. Sludge digestate enhanced tomato plant dry weight by 87%, while its nitrogen content increased by 90%. The impact of nitrogen and phosphorus contents in the digestate was strongest on tomato plant dry weight, thus explaining the efficiency of sludge digestate relative to other types of digestate. However, when methane production is considered, the combination of pre-treatment with co-digestion of macroalgal residues and sludge appears most beneficial for maximizing energy recovery and for biofertilizer generation. Unlabelled Image • In mono-digestion, KOH pretreatment of sludge led to 39% higher methane yield. • Highest yield 281 N ml/g VS from pretreated mixture of sludge and macroalgal residue • Enhancement of dry weight reached up to 87% due to digestate application. • Sludge digestate enhanced chlorophyll a of tomato plant by 84%. • Dry weight of tomato was highly correlated with N and P content in digestate. [ABSTRACT FROM AUTHOR]

For the first time, Polyporus brumalis BRFM985 was cultivated on wheat straw to investigate the simultaneous effects of pretreatment parameters on anaerobic digestion: these include initial substrate humidity, temperature, duration, and metal supplementation. Surface response methodology was applied to quantify the importance of each parameter, as well as the synergistic effects between them. Firstly, metal addition and secondly, pretreatment duration, both resulted in a positive impact. According to calculations, the highest methane production (182 dm 3 of methane per kilogram of initial Total Solids) is associated to pretreatment with metal addition during 20 days. In comparison with the least optimal conditions (118 dm 3 .kg −1 without metal addition, during 15 days), this result implies a 52% increase. [ABSTRACT FROM AUTHOR]

Waste management by anaerobic digestion generates a final byproduct, the digestate, which is usually separated into solid and liquid fractions to reduce the volume for transportation. The composition of the solid fraction has been recently studied to allow its valorization. However, full composition of liquid fraction of digestate and its size fractionation are less considered in the literature for efficient post treatment and valorization purposes. Therefore, here we characterized in detail liquid fraction of digestate obtained after solid-liquid separation from 11 full-scale co-digestion plants. The liquid fraction has a high concentration in organic matter with Chemical Oxygen Demand (COD) from 9.2 to 78 g/L with 60-96% of COD in suspended particles (>1.2 μm), 2-27% in colloids (1.2 μm to 1 kDa) and 2-18% in dissolved matter (<1 kDa). Besides, it contained from 1.5 to 6.5 g/L total nitrogen and high ions concentrations (0.5-3.1 g/L NH4+, 1.05-5.48 g/L K+, 0-2.13 g/L PO43-). In addition, liquid fraction of digestate has poor biodegradability due to presence of humic substances making aerobic treatment inefficient. Only physico-chemical post treatment can be proposed for organic matter removal. [ABSTRACT FROM AUTHOR]