Sewage sludge management is now becoming a serious issue all over the world. Anaerobic digestion is a simple and well-studied process capable of biologically converting the chemical energy of sewage sludge into methane-rich biogas, as a carbon-neutral alternative to fossil fuels whilst destroying pathogens and removing odors. Hydrolysis is the rate-limiting step because of the sewage sludge complex floc structure (such as extracellular polymeric substances) and hard cell wall. To accelerate the rate-limiting hydrolysis and improve the efficiency of anaerobic digestion, various pretreatment technologies have been developed. This paper presents an up-to-date review of recent research achievements in the pretreatment technologies used for improving biogas production including mechanical (ultrasonic, microwave, electrokinetic and high-pressure homogenization), thermal, chemical (acidic, alkali, ozonation, Fenton and Fe(II)-activated persulfate oxidation), and biological options (temperature-phased anaerobic digestion and microbial electrolysis cell). The effectiveness and relative worth of each of the studied technologies are summarized and compared in terms of the resulting sludge properties, the digester performance, the environmental benefits and the current state of real-world application. The challenge and technical issues encountered during sludge cotreatment are discussed, and the future research needs in promoting full-scale implementations of those approaches are proposed.

Overview of pretreatment strategies for enhancing sewage sludge disintegration and subsequent anaerobic digestion: Current advances, full-scale application and future perspectives

Enhanced anaerobic digestion of waste activated sludge digestion by the addition of zero valent iron

Microbial exopolysaccharides: Main examples of synthesis, excretion, genetics and extraction

Energy recovery from sewage sludge offers an opportunity for sustainable management of sewage sludge and energy. Anaerobic digestion and pyrolysis are among the most promising processes applicable for sewage sludge-to-energy conversion. Anaerobic digestion of sewage sludge forms methane-rich biogas, which can be utilized as fuel to offset heat and electricity consumption of the wastewater treatment sector. However, the digestion process has the limitation that it cannot sufficiently extract the energy in sewage sludge. The digested sludge is still energy profitable in that it contains considerable organic matter, but poor in biodegradability. Sludge pyrolysis is an innovative process that can convert both raw and digested sludge into useful bioenergy in the form of oil and gas, forming biochar as a byproduct that is environmentally resistant and holds potential for carbon sequestration and soil conditioning. It is expectable that sludge pyrolysis would step into practical deployment in the near future. This paper presents a brief overview of anaerobic digestion and pyrolysis in the application to bioenergy production from sewage sludge. An assessment of energy conversion efficiency of two parallel sludge-to-energy pathways is also presented. One pathway relies on an exclusive pyrolysis process (fed with raw sludge) while the other is based on anaerobic digestion followed by pyrolysis (fed with the digested sludge). The pathway via the combination of anaerobic digestion and pyrolysis could achieve higher energy efficiency compared to the pathway employing the pyrolysis alone.

Sewage sludge-to-energy approaches based on anaerobic digestion and pyrolysis: Brief overview and energy efficiency assessment

Heterogeneous catalytic treatment of synthetic dyes in aqueous media using Fenton and photo-assisted Fenton process

Improving anaerobic biodegradability of biological sludges by Fenton pre-treatment: Effects on single stage and two-stage anaerobic digestion

Disintegration of biological sludge: Effect of ozone oxidation and ultrasonic treatment on aerobic digestibility

Fenton process was investigated for the purpose of biological sludge disintegration. The Box-Wilson experimental design was employed to evaluate the effects of major process variables (Fe(II) and H 2 O 2 concentrations) on both disintegration and dewatering performance of sludge. Results showed that 4g Fe(II)/kg total solids (TSs) and 60 g H 2 O 2 /kg TS are efficient for floc disintegration. Fenton pre-treatment enhanced the biodegradability of sludge. For 4 g Fe(II)/kg TS and 60 g H 2 O 2 /kg TS, 19.4% higher methane production was achieved compared to raw sludge in biochemical methane potential assay. Fenton pre-treatment resulted in the release of organic sludge components into the liquid phase. For 4 g Fe(II)/kg TS and 60 g H 2 O 2 /kg TS, dissolved organic carbon and total nitrogen in sludge's supernatant increased by 75.74 and 60.60%, respectively. Fenton pre-treatment enhanced the filterability of sludge and it can be applied for conditioning purpose before mechanical dewatering units.

Effects of Fenton Pre‐Treatment on Waste Activated Sludge Properties

Microplastics are widely detected in wastewater treatment plants. They can remove microplastics from wastewaters with a high yield, but it means that microplastics are transferred and accumulated to sewage sludge. Lately, increasing attention has been paid to microplastics in raw and treated wastewaters. However, studies about quantification and identification of microplastics in sewage sludge are very scarce and need to be further investigated. Since the sludge-based microplastics are newly studied and are a challenging matrix due to high organic content, there is limited knowledge of sampling, pre-treatment methods, identification techniques, and expression units. Besides, treated sewage sludge is mostly used for soil amendment to improve soil fertility and it gives economic advantages. This situation creates a pathway for microplastics entering the soil environment with unknown consequences. To the best of our knowledge, microplastics have a large specific surface area, small size, and hydrophobicity which makes it a good adsorbent for other pollutants. Therefore, the combined effect of microplastics with adsorbed pollutants such as heavy metals, antibiotics, and persistent organic pollutants could give serious harm to soil safety and soil organisms. Herein, new developments in the methods for sampling, pre-treatment, and identification techniques of microplastics in sewage sludge were reviewed. Then, the abundance of microplastics, major polymer types, and shapes in sewage sludge were examined. Finally, the effects and ecological risks of microplastic pollution as a result of agricultural usage of sewage sludge in the soil environment have been summarized. Also, the main points for future research were highlighted.

Sampling, pre-treatment, and identification methods of microplastics in sewage sludge and their effects in agricultural soils: a review.

Meat processing wastewater sludge has high organic content but it is very slow to degrade in biological processes. Anaerobic digestion may be a good alternative for this type of sludge when the hydrolysis, known to be the rate-limiting step of biological sludge anaerobic degradation, could be eliminated by disintegration. This investigation deals with disintegration of meat processing wastewater sludge. Microwave (MW) irradiation and combined alkaline pretreatment and MW irradiation were applied to sludge for disintegration purposes. Disintegration performance of the methods was evaluated with disintegration degree based on total and dissolved organic carbon calculations (DD TOC), and the solubilization of volatile solids (S VS) in the pretreated sludge. Optimum conditions were found to be 140°C and 30 min for MW irradiation using response surface methodology (RSM) and pH=13 for combined pretreatment. While DD TOC was observed as 24.6% and 54.9, S VS was determined as 8.54% and 42.5% for MW pretreated and...

Gülbin Erden

Papers

Improving anaerobic biodegradability of biological sludges by Fenton pre-treatment: Effects on single stage and two-stage anaerobic digestion

Disintegration of biological sludge: Effect of ozone oxidation and ultrasonic treatment on aerobic digestibility

Effects of Fenton Pre‐Treatment on Waste Activated Sludge Properties

Sampling, pre-treatment, and identification methods of microplastics in sewage sludge and their effects in agricultural soils: a review.

Combination of alkaline and microwave pretreatment for disintegration of meat processing wastewater sludge.