Which pretreatment techniques enhance anaerobic digestion of organic solid waste?
This paper reviews pretreatment techniques to enhance the anaerobic digestion of organic solid waste, including mechanical, thermal, chemical and biological methods. The effects of various pretreatment methods are discussed independently and in combination.
What is aerobic pretreatment for wastewater treatment?
The very short story with aerobic pretreatment is adding a lot of air to a wastewater tank, this provides oxygen to bacteria and those bacteria consume the sugar and alcohol (BOD) in your wastewater, thereby treating the wastewater. Sounds easy, but remember people get PhD’s in this stuff.
What are the stages of anaerobic digestion in wastewater treatment?
Three stages are known to occur in the biological action involved in the process of digestion of sludge for anaerobic digestion wastewater treatment. These are (1) acidification (2) lysis/ liquefaction or a period of acid digestion and (3) gasification or conversion of acids into methane and carbon dioxide.
Is thermal pretreatment more cost-effective than two-stage anaerobic digestion?
Based on the comparison, thermal pretreatment at low (<110 °C) temperatures and two-stage anaerobic digestion methods result in a more cost-effective process performance as compared to other pretreatment methods. 1. Introduction Anaerobic digestion (AD) is one of the oldest and well-studied technologies for stabilizing organic wastes [1].
What is anaerobic digestion pretreatment?
Mechanical pretreatment disintegrates and/or grinds solid particles of the substrates, thus releasing cell compounds and increasing the specific surface area. An increased surface area provides better contact between substrate and anaerobic bacteria, thus enhancing the AD process [3], [24], [25].
What are the three pretreatment methods that impact anaerobic digestion?
Several pretreatment methods of organic wastes prior to anaerobic digestion have been reported, these include mechanical, thermal, chemical, biological and hybrid (combination of more than one method) methods.
Why pretreatment is done for a substrate in anaerobic digestion process?
Overcoming the substrate barriers via pre-treatment may potentially improve the AD system by enhancing operational stability, increasing methane yields and solids reduction under similar operating conditions to those without pre-treatment or by increasing methane productivity by allowing reductions in hydraulic ...
What is sludge pretreatment?
Pretreating sludge upstream of the anaerobic digestion (AD) is sometimes carried out to improve the sludge biological treatability. This is usually achieved through heat treatment, and referred to as thermal conditioning. Thermal conditioning is especially favoured for waste activated sludge (WAS) sources.
What is pretreatment step?
Pre-treatment is the removal of specific pollutants from produced water before mixing it with the main produced water stream, wherein the recovery of some contaminants may occur. From: Journal of Water Process Engineering, 2014.
Why pretreatment of biomass is required?
Pretreatment is an important tool for cellulose conversion processes, and is essential to change the structure of cellulosic biomass to make cellulose more available to the enzymes that convert the carbohydrate polymers into fermentable sugars (Mosier et al.
What is pretreatment process of biomass?
The process that converts any source of lignocellulosic biomass from its native form, which is recalcitrant to hydrolysis with cellulase enzyme systems, into a form which enzymatic hydrolysis is effective is referred to as 'pretreatment' in bioprocess engineering (Lynd et al. 2002).
What is the function of pre treatment chemical?
Typical goals of pretreatment include (1) production of highly digestible solids that enhances sugar yields during enzyme hydrolysis, (2) avoiding the degradation of sugars (mainly pentoses) including those derived from hemicellulose, (3) minimizing the formation of inhibitors for subsequent fermentation steps, (4) ...
What is the best pre treatment of lignocellulosic materials for ethanol production?
One of the crucial steps in the ethanol production is the hydrolysis of the hemicellulose and cellulose to monomer sugars. The most promising method for hydrolysis of cellulose to glucose is by use of enzymes, i.e. cellulases.
What is feed pretreatment?
In general, the feed pre-treatment technologies are focused on achieving the following objectives: Removing toxic, inhibitory and unwanted substance for digester. Reducing digester maintenance and clean up. Homogenizing the feedstock mixture.
How does pretreatment affect feedstock?
Pre-treatments expose and increase the surface area of these feedstocks by breaking them down further and thus increasing the organic loading rates and reducing the required retention time in the digester. So, pre-treatment can be generally divided into the following three categories:
What happens if you don't remove contaminants?
These contaminants, If not removed, can cause damage to the downstream processes and equipments; for example excessive grit and sand can settle in the digester bottom, clog pipes and damage process valves and sensors.
Is hydrolysis anaerobic or anaerobic?
Hydrolysis Enhancement and Process Improvement: It is widely stated that hydrolysis is one of the rate limiting steps for anaerobic digestion especially in the presence of complex organic compounds in the feedstocks- Read More.
Sustainable Sewage Sludge Management and Resource Efficiency
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Abstract
Sustainable energy production is the major priority in the world due to global warming, climate change, and fossil fuels depletion. Anaerobic digestion (AD) of sludge is the sustainable process producing the energy and minimizing the fossil fuel usage.
1. Introduction
The production of inevitable waste activated sludge (WAS) as a by-product during the biological wastewater treatment demands for sustainable treatment options that assist in the proper utilization of sludge before its disposal.
2. Pretreatment technologies
The pre-treatment technologies enable the cells constituents easily available for the microorganisms to produce the biogas. Various pre-treatment technologies (mainly mechanical, chemical, biological, and physio-chemical) and their effect on enhancing the AD and methane production presented in the literature during last decade are discussed here.
3. Other different pre-treatment methods
Integration of pre-treatment methods has also been studied for sludge stabilization to further improve AD and biogas production. A combination of thermal and chemical pre-treatment methods is known to improve the degradation of volatile solids and biogas production [ 108 ].
4. Feasibility of a full-scale application
With an ever-increasing concern for the environment, different pre-treatment methods can enhance the AD performance. Nevertheless, the high capital cost, high consumption of energy, required chemicals, and sophisticated operating conditions (maintenance, odor control, etc.) are the major factor hindering their full-scale application [ 123 ].
5. Conclusion
The pre-treatment methods have the potential to solubilize complex sludge components which include the organic matter, EPS, and the microbial cell wall which in turn makes the progression of subsequent biological degradation treatments easier. AD is the sustainable process widely employed for bioenergy generation from the WAS.
What is the purpose of anaerobic digesters in wastewater treatment?
Existing Infrastructure – Many wastewater treatment facilities in the Pacific Southwest (US Region 9) and across the country, use anaerobic digesters to reduce the volume of the biosolids (sewage sludge) before they are taken off site.
What is anaerobic digestion?
There are two distinct uses of Anaerobic Digestion in Wastewater Treatment: 1 As a treatment process in its own right for primary sewage treatment/ organic industrial effluent, as known as a “UASB” 2 As a method of treating the sludge produced by Wastewater Treatment Plants.
What are the stages of digestion of sludge?
These are (1) acidification (2) lysis/ liquefaction or a period of acid digestion and (3) gasification or conversion of acids into methane and carbon dioxide.
What is sludge digested?
The digested sludge is de-watered, dried up and used as sewage sludge fertilizer while the gases produced are used as fuel or for driving gas engines. The supernatant liquor is re-treated at the treatment plant along with the raw sewage. The tanks in which sludge digestion is carried out are called sludge digestion tanks.
What is the stage of methane gasification?
It is the stage when more resistant materials like proteins and organic acids are broken up. Large volumes of methane gas of high calorific value, along with comparatively smaller volumes of carbon dioxide are evolved. The pH value goes to the alkaline range i.e., above 7 and a tarry odour appears. Gasification finally becomes very slow; the sludge becomes well adjusted and is stable enough for disposal. This stage in the digestion of sludge is also termed as alkaline fermentation.
What happens when a wastewater plant accepts food waste?
infrastructure at the wastewater plant. When a facility accepts food waste at a plant, they can charge the waste hauler a tipping fee for accepting the material. In addition, there is a significant amount of money that will be saved in. energy avoidance due to methane production.
What are the products of decomposition of sewage sludge?
The products of decomposition are acid carbonates, organic acids with gases as carbon dioxide and hydrogen sulfide.
What is anaerobic digestion?
Anaerobic digestion (AD) is one of the oldest and well-studied technologies for stabilizing organic wastes [1]. Among the treatment technologies available for treating organic solid wastes (OSW), AD is very suitable because of its limited environmental impacts [2], [3], [4], [5] and high potential for energy recovery [2], [3], [6]. Such positive aspects coupled with the recent concerns on rapid population growth, increasing energy demand, and global warming have promoted further research on the AD process development and improvement in order to enhance biogas production, achieve faster degradation rates and reduce the amount of final residue to be disposed [3], [4], [7].
What is chemical pretreatment?
Chemical pretreatment is used to achieve the destruction of the organic compounds by means of strong acids, alkalis or oxidants. AD generally requires an adjustment of the pH by increasing alkalinity, thus alkali pretreatment is the preferred chemical method [71].
Why is acid pretreatment important?
Acid pretreatment is more desirable for lignocellulosic substrates, not only because it breaks down the lignin, but also because the hydrolytic microbes are capable of acclimating to acidic conditions [76]. The main reaction that occurs during acid pretreatment is the hydrolysis of hemicellulose into perspective monosaccharides, while the lignin condensates and precipitates [34], [77]. Strong acidic pretreatment may result in the production of inhibitory by-products, such as furfural and hydroxymethylfurfural (HMF) [73], [76]. Hence, strong acidic pretreatment is avoided and pretreatment with dilute acids is coupled with thermal methods (see also Section 2.5). Other disadvantages associated with the acid pretreatment include the loss of fermentable sugar due to the increased degradation of complex substrates, a high cost of acids and the additional cost for neutralizing the acidic conditions prior to the AD process [73], [78], [79].
What are the reactions of alkali pretreatment?
During alkali pretreatment, the first reactions that occur are solvation and saphonication, which induce the swelling of solids [31]. As a result, the specific surface area is increased and the substrates are easily accessible to anaerobic microbes [34], [73], [74]. Then, COD solubilization is increased through various simultaneous reactions such as saponification of uronic acids and acetyl esters, as well as neutralization of various acids formed by the degradation of the particulates [75]. When substrates are pretreated with alkali methods, an important aspect is that the biomass itself consumes some of the alkali [34], thus higher alkali reagents might be required for obtaining the desired AD enhancement.
What is a TPAD digester?
This method usually consists of a primary digester at thermophilic (or hyper-thermophilic) temperature followed by a mesophilic secondary digester. The advantages of TPAD include not only higher methane production yields, but also a pathogen free high nutrient digestate [114]. Riau et al. suggested that TPAD is preferred if the purpose is to achieve pathogen free digestate, which can be directly used as soil conditioner [115].