When the sludge reduction technique is applied to the return sludge, the treatment produces biodegradable carbonaceous matter supporting denitrification in activatedsludge stages. When it is integrated in the sludge handling units, improvements in biogas production and sludge stabilisation in anaerobic digesters are obtained.
Full Answer
Does sludge production affect wastewater treatment strategies?
Sludge is a carrier of energy and nutrients, and future-oriented wastewater treatment strategies are focused on the recovery of biomass energy and nutrients from sludge ( Logan and Rabaey, 2012 ). Greater sludge production has the obvious benefit of promoting energy self-sufficiency during wastewater treatment.
How does the sludge reduction technique work?
When the sludge reduction technique is applied to the return sludge, the treatment produces biodegradable carbonaceous matter supporting denitrification in activatedsludge stages. When it is integrated in the sludge handling units, improvements in biogas production and sludge stabilisation in anaerobic digesters are obtained.
Are there alternative technologies to reduce sludge production?
Many studies have been produced since the ‘90s on alternative technologies for direct on-site reduction of sludge production (as dry mass and not only in volume). The proposed methods are based on physical, mechanical, chemical, thermal and biological treatments.
Is autotrophic growth beneficial to sludge reduction during wastewater treatment?
Autotrophic growth leads to a relatively low biomass yield due to the resulting slow growth rate and high maintenance energy requirement ( Strous et al., 1998 ). The low biomass yield associated with autotrophic growth is beneficial to sludge reduction during wastewater treatment.
How do you reduce sludge production in wastewater treatment?
The new wastewater treatment processes including SANI®, high-rate activated sludge coupled autotrophic nitrogen removal and anaerobic membrane bioreactor coupled autotrophic nitrogen removal also have a great potential to reduce sludge production.
What is sludge reduction?
the recovery of materials or energy from sludge, if sludge is considered a resource; the reduction of the amount of sludge produced, if sludge is considered waste.
What is sludge dewatering in wastewater treatment?
Sludge dewatering is the practice of minimizing waste by volume to prepare for its effective disposal. Sludge originates during the process of treating wastewater before the water can be released back into the environment.
Why is sludge treatment necessary?
Two basic goals of treating sludge before final disposal are to reduce its volume and to stabilize the organic materials. Stabilized sludge does not have an offensive odour and can be handled without causing a nuisance or health hazard. Smaller sludge volume reduces the costs of pumping and storage.
What are the methods of sludge disposal?
Methods of Removing SludgeThickening. It is usually the first step in treating sludge as it is not possible to handle thin sludge as it is a slurry of solids suspended in water. ... Sludge Digestion. ... Dewatering. ... Disposal. ... Anaerobic digestion.
How much sludge is produced in wastewater treatment?
A WWTP produces about two litres of raw sludge per person per day.
Which of these processes am to reduce water content from the water treatment sludge?
Detailed Solution The Correct Answer is Sewage treatment.
How does activated sludge treatment help in secondary treatment?
Activated sludge is a common suspended-growth method of secondary treatment. Activated sludge plants encompass a variety of mechanisms and processes using dissolved oxygen to promote growth of biological floc that substantially removes organic material.
What are the advantages of activated sludge process?
Advantages of Activated Sludge ProcessLow installation cost.Good quality effluent.Low land requirement.Loss of head is small.Freedom from fly and odor nuisance high degree of treatment.
Why is sludge dewatering necessary?
It's vital to employ technical applications such as dewatering to reduce these expenses. Sludge dewatering helps cut down on disposal costs by reducing the volume of water-saturated soil. It can also help save between 75 to 80 percent of transportation and storage expenses.
How would the wastewater sludge affect the environment if applied to the land?
Environmental issues related to the recycling of sewage sludge on land include the risk of nutrient leaching, impacts on soil biodiversity and greenhouse gas emissions. Methane and nitrous oxide, both potent greenhouse gases, are both produced after sludge and other bio-wastes and recycled into agricultural land.
What are the consequences of sludge production?
As a consequence of the sludge production which is increasing, whereas disposal routes are narrowing, is a progressive further rising in costs. There are two aims with regard to sludge: the reduction of the amount of sludge produced, if sludge is considered waste.
What are the objectives of sludge solubilization?
Most of them are aimed at solids solubilisation and disintegration of bacterial cells in sludge, with the objectives of: reducing sludge production directly in the wastewater handling units; reducing sludge mass in the sludge handling units and simultaneously improving biogas production in anaerobic digestion or, in some cases, dewaterability;
How much sludge is produced in a WWTP?
The volume of sludge produced in a WWTP is only about 1% (dewatered sludge is 0.5‰) of the volume of influent wastewater to be treated. To manage WWTPs effectively and efficiently, it is absolutely necessary to extract waste sludge, including inert solids and excess biomass, in order to prevent their accumulation within the system.
What temperature does sludge need to be to be oxidized?
Once produced, the sludge can undergo hydrothermal oxidation processes to reduce the amount requiring disposal. The sludge mineralisation using oxygen can be achieved at high temperature (>850°C) in the gaseous phase (incineration) or at a relatively low temperature (in the range 150-320°C or >374°C) in the liquid phase: water (subcritical or supercritical) is used as a reaction medium. Two hydrothermal oxidation processes are available: (1) subcritical water oxidation, including wet air oxidation; (2) supercritical water oxidation.
Is sludge considered waste?
the reduction of the amount of sludge produced, if sludge is considered waste. For many producers, there are not enough economic advantages to make beneficial reuse of sludge an attractive investment. Even though a sludge-zero process remains the utopia in sludge management, a more realistic and feasible practice is to continue to reduce ...
Does biodegradability increase in inert solids?
Biodegradability increase in inert solids. A further mechanism, which is linked to biodegradability increase of inert solids, can be considered, even though it can not be considered a separate mechanism because it takes place in combination with other mechanisms.
How to dispose of municipal solid waste?
The main method used to dispose of municipal solid waste (MSW) is to place it in a “landfill”—also called a “garbage dump” or a “rubbish tip”— 85 to 90% of domestic waste and commercial waste is disposed of in this way. If the landfill is suitably aerated and if it has sufficient amounts of organic waste, aerobic degradation naturally sets in. Depending on the components of the landfill, i.e., if it has sufficient amounts of organic matter with no toxic chemicals, then both aerobic and anaerobic degradation set in. Initially anaerobic degradation produces volatile carboxylic acids and esters, which dissolve in the water that is present. In the next stage of decomposition, significant quantities of methane gas (biogas) are released as these acids and esters are degraded to methane and carbon dioxide. The presence of heavy metals and polyhalogenated aromatics dampen the growth of microorganisms. Care must be taken to ensure that these pollutants are pretreated before being dumped into the landfill. Another way to overcome the presence of these growth retardants is to inoculate the landfill with microorganisms adapted to high concentrations of these toxins. One of the major problems of landfills is the leachate —water seepage from the landfill. This leachate contains organic, inorganic, and microbial contaminants extracted from solid waste, which may contaminate the groundwater. Aerobic degradation is the typical treatment for rapidly decreasing the biological oxygen demand (BOD) of the leachate. In the past, landfills were often simply “holes in the ground” that had been created by mineral extraction. Modern municipal landfills are much more highly designed and engineered. Anaerobic digestion is gaining more acceptance in the treatment of solid wastes. The high solids reactor concept for anaerobic digestion can handle more than 30% dry solids in the feed material and achieve a high conversion of organics to methane ( Rivard, 1993 ).
What is compost bioremediation?
Compost bioremediation refers to the use of a biological system of microorganisms in a mature, cured compost to sequester or break down contaminants in soil. Microorganisms digest, metabolize, and transform contaminants in soil and ground into humus and inert byproducts, such as carbon dioxide, water, and salts. Compost bioremediation has proven effective in degrading or altering many types of contaminants such as chlorinated and nonchlorinated hydrocarbons, wood-preserving chemicals, solvents, heavy metals, pesticides, petroleum products, and explosives. The compost used in bioremediation is referred to as “tailored” or “designed” compost in that it is specially made to treat specific contaminants at specific sites. In addition to reducing contaminant levels, compost advances this goal by facilitating plant growth. In this role, compost provides soil conditioning and also provides nutrients to a wide variety of vegetation. In 1979, at a denuded site near the Burle Palmerton zinc smelter facility in Palmerton, PA (United States), a remediation project was started to revitalize 4 square miles of barren soil that had been contaminated with heavy metals. Researchers planted Merlin Red Fescue, a metal-tolerant grass, in lime fertilizer and compost made from a mixture of municipal wastewater treatment sludge and coal fly ash. The remediation effort was successful, and the area now supports a growth of Merlin Red Fescue and Kentucky Bluegrass (Chaney, 1994 ). A similar success story was observed for the remediation of soil contaminated with petroleum hydrocarbons ( Fordham, 1995 ).
What are the biota in activated sludge?
The biota present in activated sludge consist of bacteria, archaea, protozoa, and metazoa as well as viruses ( Rittmann and McCarty, 2012 ). Of these, bacteria represent the main components of the activated sludge community. These bacteria mainly include nitrifiers [ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB)], denitrifiers, and phosphorus-accumulating organisms (PAOs), all of which play important roles in nutrient removal ( Rittmann and McCarty, 2012 ). Filamentous bacteria function as a backbone in the structure of the floc ( Andreadakis, 1993 ). Through predation, protozoan and metazoan species participate in balancing the ecosystem in activated sludge systems; these species are quite sensitive to physical, chemical, and operational processes ( Ginoris et al., 2007 ). Substances and energy are transferred from substrates to bacteria and then to protozoans or metazoans through the food chain in the wastewater treatment system ( Elissen et al., 2006 ). Energy is lost due to inefficient biomass conversion during energy transfer from low to high trophic levels ( Rittmann and McCarty, 2012 ). Under the optimal conditions, the total energy loss will be maximal and the total biomass production will thus be minimal. Therefore, the predation of microfauna on bacteria can reduce sludge production.
What is anaerobic side stream reactor?
The anaerobic side-stream reactor (ASSR) process has received extensive attention due to its excellent sludge reduction, nutrient removal and sludge settling property. The main difference between the ASSR and OSA configurations is the reduced space requirement in the mainstream due to absence of secondary settling and an alternate, rather than continuous, loading mode ( Ferrentino et al., 2016a ). There is debate regarding the mechanism of achieved sludge reduction when using activated sludge with an ASSR. Different mechanisms have been proposed to be occurring in the ASSR, including cryptic growth, metabolism of slow-growing microorganisms, uncoupling metabolism, and destruction of EPS ( Ferrentino et al., 2016b ). In particular, cryptic growth has received widespread attention. Previous studies have highlighted its contributions to sludge reduction in ASSR processes and thus are the main mechanisms discussed in this review.
Sludge Production
Wastewater Handling Units
- In the wastewater handling units in a WWTP the types of sludge produced are: 1. primary sludge– produced by settleable solids removed from raw wastewater in primary settling; characterised by high putrescibility and good dewaterability when compared to biological sludge; TS content in primary sludge is in the range 2-7% (Turovskiy and Mathai, 2006); 2. secondary sludge(also calle…
Sludge Handling Units
- In the sludge handling units, a combination of any two or three of the above types is introduced. During the biological treatment of wastewater, in addition to cell biomass, a large amount of non-biodegradable (inert) solids in particulate form, incoming with the influent raw wastewater, contributes significantly to sludge production. The presence of inert organic solids in sludge is d…
Principles of Sludge Reduction Techniques
- The cost for treatment + disposal of sludge in European countries has been estimated to reach, on average, approximately 500 € per tonne of dry mass, according to the type of treatment and disposal, but a further increase is expected in the near future. As a consequence of the sludge production which is increasing, whereas disposal routes are narrowing, is a progressi…
Mechanisms in Sludge Reduction Techniques
- The various mechanisms exploited in the sludge reduction techniques are identified and schematically indicated in the figure.
Cell Lysis and Cryptic Growth
- The term “cryptic growth” indicates the reutilisation of intracellular compounds (both carbonaceous compounds and nutrients) released from cell lysis, for the growth of viable cells of the same population. Some sludge reduction techniques cause cell lysis with the consequent solubilisation of cellular constituents, which become substrate available for further biodegradati…
Uncoupled Metabolism
- The term “uncoupling” defines the inability of oxidative phosphorylation to generate the maximum theoretical quantity of metabolic energy in the form of ATP. The uncoupled metabolism increases the discrepancy in the energy level between catabolism and anabolism, limiting the energy available for anabolism. As a consequence, bacteria first satisfy their maintenance functions be…
Endogenous Metabolism
- The concept of the endogenous metabolism describes the observation that storage compounds are used for maintenance purposes when the external substrate is completely depleted. In other words, endogenous metabolism should be defined as a state when no net growth is possible, but cells consume energy to remain viable. By increasing energy requirements for non-growth activit…
Microbial Predation
- Bacteria are a food source for higher organisms, such as protozoa and metazoa. When one organism eats another the total amount of biomass decreases and the transfer to a higher trophic level of the food chain occurs. In this way part of the biomass and the potential energy is lost as heat and excretory products, which causes a reduced growth of biomass and lower sludge prod…
Biodegradability Increase in Inert Solids
- A further mechanism, which is linked to biodegradability increase of inert solids, can be considered, even though it can not be considered a separate mechanism because it takes place in combination with other mechanisms. For example, ozonation is expected to be a strong oxidant on all sludge components: whether cellular biomass or inert compounds. This treatment on cell…