What is sludge and how it is treated?
The residue that accumulates in sewage treatment plants is called sludge (or biosolids). Sewage sludge is the solid, semisolid, or slurry residual material that is produced as a by-product of wastewater treatment processes. This residue is commonly classified as primary and secondary sludge. Primary sludge is generated from chemical precipitation, sedimentation, and other primary processes, whereas secondary sludge is the activated waste biomass resulting from biological treatments.
How to treat and dispose sludge?
- Increases solids content to 15 to 30%
- Air drying reduces pathogens
- Centrifugation and filtration result in some loss of nutrients
What happens to sludge from a wastewater treatment facility?
Wastewater then enters the second section or sedimentation tanks. Here, the sludge (the organic portion of the sewage) settles out of the wastewater and is pumped out of the tanks. Some of the water is removed in a step called thickening and then the sludge is processed in large tanks called digesters. 5. Removing scum
What are the methods of sludge disposal?
Ultimate Disposal of Sludge:
- Landfilling: Landfilling is a method for the final disposal of sludge that is not useful any more. ...
- Lagooning: A lagoon is a shallow lake (or earth basin) usually located near a river or a sea. ...
- Septage and Septage Disposal: Septage is a combination of sludge, scum and liquid coming out from a septic tank. ...
Why sludge treatment is done?
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 type of treatment is activated sludge?
biological wastewater treatment processThe activated sludge process is a type of biological wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa.
What is Sludge Treatment focus?
Some key sludge processing methods are intended to stabilise the sludge. Sludge stabilisation processes are those which reduce/eliminate its odour, putrescence (i.e. it's tendency to decay) and its pathogenic (disease-causing) micro-organism content.
What is sludge used for?
Once sludge is treated, it can safely be used, as fertilizer or for controlling soil erosion, among other uses. If it is not treated, it can be hazardous, not only to those who touch it, but also the land upon which it is disposed as well as on any crop on such land.
What is activated sludge treatment process?
The activated sludge process is a means of treating both municipal and industrial wastewater. The activated sludge process is a multi-chamber reactor unit that uses highly concentrated microorganisms to degrade organics and remove nutrients from wastewater, producing quality effluent.
What is ASP treatment?
The Activated Sludge Process (ASP) is a sewage treatment process in which air or oxygen is blown into raw, unsettled sewage to smash the solids and develop a biological 'soup' which digests the organic content and pollutants in the sewage.
What is sludge example?
Sludge definition Sludge is a substance that is between solid and liquid form. An example of sludge is a mass of mud formed in a river bed after a flood. An example of sludge is the treated material from a sewage plant.
What happens to the water after treatment?
What happens to the treated water when it leaves the wastewater treatment plant? The treated wastewater is released into local waterways where it's used again for any number of purposes, such as supplying drinking water, irrigating crops, and sustaining aquatic life.
What sludge means?
Definition of sludge 1 : mud, mire especially : a muddy deposit (as on a riverbed) : ooze. 2 : a muddy or slushy mass, deposit, or sediment: such as. a : precipitated solid matter produced by water and sewage treatment processes. b : muddy sediment in a steam boiler.
In which sludge treatment process the sludge is treated with chemicals?
There are various options for treating sludge including stabilization, thickening, dewatering, drying, and incineration. The costs for treating sludge and removing sludge from wastewater are roughly the same. Typically a polymer chemical is used for the volume reduction process known as dewatering.
What is the most common form of sludge treatment?
The commonest form of biological sludge treatment on large works is anaerobic digestion (AD), in which sludge is held in a mixed tank in the absence of oxygen.
What is activated sludge treatment?
The activated sludge treatment is conventional process used in WWTPs which involves the physically pretreated wastewater from different sources and microorganisms to remove nutrients and oxidized recalcitrant organic compounds. This process has been divided into following steps: (i) after pretreatment the wastewater is treated with aerobic bacteria in an aerated chamber, where the retention time is being adjusted to ensure that effluent is sufficiently treated before entering into the next step for settlement, (ii) the effluent of aeration tank enter into settlement tank to undergo solid/liquid separation, (iii) the treated water is being released and the collected activated sludge is mainly recycled back to the aeration tank to maintain the active microorganisms to carry on the treatment process all again.
What is the most thorough degree of sewage sludge processing?
Sludge treatment centered on incineration can achieve the most thorough degree of sewage sludge processing from the perspectives of quantity reduction, stabilization, harmless treatment, and reutilization.
How is sludge dried?
In the conventional drying and incineration process, the drying and incineration operations are separated. The sludge is first dried in one equipment and then incinerated in another incinerator. The heat for sludge drying may be from burning of oil, natural gas, coal, and even electricity. The heat from the dry sludge is also used for the sludge drying. To raise the heat utilization efficiency, some equipment makes the hot flue gas from coal combustion direct contact with sludge. In this case, the oxygen content in the drying system must be controlled very carefully, otherwise explosion may occur. Indirect drying process will lead to a lower heat utilization efficiency and thus will raise the cost.
How to carbonize sludge?
Drying and incineration can totally carbonize organic constituents in sludge and minimize the volume of sludge (90% reduction). The chemical energy in the dried sludge can be harvested during combustion and subsequently employed for thermal drying. Nonetheless, thermal drying is not a cheap option because of its high energy demand to remove biologically bound water from sludge. The economics of the process depend upon dry matter content, VS/TS (total solids) ratio, and calorific value ( Fig. 1.9 ). Meanwhile, the resulting combustion ash can be used as a raw material for the manufacture of different building materials such as sintered bricks, tiles, pavers, or Portland cement if it is justified as a general waste other than a hazardous waste.
Where is the Lartington sludge treatment plant?
Progressing cavity pumps have increased the efficiency of sludge treatment at Northumbrian Water's Lartington Sludge Treatment Works in Cotherstone, U.K. (Fig. 64 ). Rain water from the Grasholme and Hury reservoirs in the Tees Valley gravitates to Lartington Water Treatment Works (WTW), where it is treated and distributed throughout the Tees Valley, principally to Darlington and Stockton. Part of this treatment involves the removal of peat-based solids from the water. The resultant sludge is sent up to the Lartington Water Treatment Works at Cotherstone, U.K.
How long does it take for sewage to be pumped into the UK?
Traditionally, the process was unheated, operating at ambient temperatures, but there are only a few such plants operating nowadays in the United Kingdom, as the process takes 2–3 months at UK temperatures.
What is sludge treatment?
When the wastewater is treated and discharged to a watercourse, the job is not over. Left behind the solids suspended in water are commonly called sludge.
Sludge Processing
Sludge is the main waste stream generated from water purification, both water for drinking and wastewater for environmental discharge.
Sources of sludge
The first source of sludge is the suspended solids that enter the treatment plant and are partially removed in the primary settling tank and clarifier.
Sludge Stabilization –
The objective of stabilization is to reduce the problems associated with two detrimental characteristics- sludge odor and presence and the presence of pathogenic organisms.
Sludge thickening-
Sludge thickening is a process in which the solid concentration is increased and the total sludge volume is correspondingly decreased, but the sludge still behaves like a liquid instead of a solid.
Sludge dewatering –
Dewatering differs from thickening in that the sludge should behave as a solid after it has been dewatered. Dewatering is seldom used as an intermediate process unless the sludge is to be incinerated and most wastewater plants use dewatering as a final method of volume reduction before ultimate disposal.
Ultimate disposal –
The option for the ultimate disposal of sludge is limited to air water and land. The strict control of air pollution is complicated although this certainly is an option.
How are sludge solids concentrated?
Sludge solids are concentrated either by settling due to gravity or by introducing air, which causes sludge solids to float.
How long does sludge stay in the air?
One of the most widely used methods for sludge treatment. Sludge is held in the absence of air for 15 to 60 days at temperatures of 68 to 131°F. Anaerobic bacteria feed on the sludge, producing methane and carbon dioxide. In some treatment plants, the methane is collected and burned to maintain the treatment temperature.
How much sewage sludge does Pennsylvania produce?
This means that Pennsylvania's POTWs generate approximately 300,000 tons of sewage sludge (dry weight basis) each year.
What is biosolids in sewage?
The term "biosolids" also helps to distinguish sewage sludge from industrial sludge by emphasizing that the former is produced by a biological process.
What is biosolids in wastewater treatment?
The industry defines biosolids as sewage sludge that has undergone sufficient treatment for stabilization and pathogen reduction, and that is of sufficiently high quality to be land applied. The term is intended to distinguish high-quality, treated sewage sludge from raw sewage sludge and from sewage sludge that contains large quantities of environmental pollutants. The term "biosolids" also helps to distinguish sewage sludge from industrial sludge by emphasizing that the former is produced by a biological process. The term has been criticized by some as an attempt to disguise the real nature of sewage sludge, thereby making land application of this material less objectionable to the general public. Although "biosolids" undoubtedly does not conjure up the same negative images as does "sewage sludge" or simply "sludge," it is a legitimate and functional term when correctly used to make the distinction described above. In this document, "sewage sludge" will be used to refer to wastewater treatment solids generally, and "biosolids" will be used to refer specifically to material that is suitable for land application.
How does incineration affect sewage?
Sewage sludge incineration reduces the volume of the material to be disposed of, completely destroys pathogens, decomposes most organic chemicals, and recovers the small amount of heat value contained in sewage sludge. The residual ash is a stable, relatively inert, inorganic material that has just 10 to 20% of the original sludge's volume. Most trace metals in the sewage sludge become concentrated in the ash (a five- to tenfold increase in concentration). This material most commonly is landfilled, although it potentially could be used in construction materials.
How long does it take for a sludge to increase pH?
Sufficient alkaline material, most commonly lime (CaO), is added to the sludge to increase its pH to at least 12 for 2 hours. The pH must remain above 11.5 for an additional 22 hours.
What is the treatment of sludge?
Conditioning: Treating the sludge with chemicals or heat so that the water can be readily separated.
What is the purpose of sludge stabilization?
The principal purposes of sludge stabilization are to breakdown the organic solids biochemically to reduce pathogens, offensive odours, potential for putrefaction and production of biogas.
What is the temperature of dewatering sludge?
Another conditioning approach is to heat the sludge at high temperatures (175-230 oC) and pressures (1000-2000 kPa). Under such conditions, water that is bound up to solids is released thus improving dewatering characteristics. The process has the disadvantage of relatively complex operation and maintenance.
How is sludge dewatered?
Most popular method of Sludge Dewatering. Sludge is pumped onto drying bed surface and allowed to dry to desired final solid concentration. Dewatered sludge is removed either mechanically or manually.
How long does it take for sludge to dry?
Sludge is applied on the sand bed and is allowed to dry by evaporation and drainage of excess water over a period of several weeks depending on climatic conditions. Bacterial decomposition of the sludge takes place during the drying process while moisture content is sufficiently high.
What is sustainable sludge handling?
Sustainable sludge handling may be defined as a socially acceptable, cost effective method that meets the requirement of efficient recycling of resources while ensuring that harmful substances are not transferred to humans or the environment.
How much volume reduction is needed for thickening?
The goal of thickening is to increase the solid content percentage of sludge by removing as much water as possible. Volume reduction of 30 to 80 percent may be achieved. The process offers a low cost solution to reduce sludge volume to be dealt with by a factor of two or more.
Does AD produce sludge?
As with AD, the process produces a relatively stable sludge end product and reduces the pathogenic content.
Is digested sludge dewaterable?
Also, the digested sludge is not as readily dewaterable mechanically. As with AD, aerobic digestion can be designed as a single or multi-tank process, with the multi-tank process providing greater process efficiency by reducing the required solids residence time.
Overview of Sludge Processing
Sludge Processing Methods
- There are essentially two methods by which the volume of sludge is reduced: 1. consolidation, which reduces the sludge volume by removing the water along with the associated dissolved solids, and 2. destruction, in which the organic carbon component of the sludge is either oxidised, ultimately to carbon dioxide, or reduced, predominantly to methane...
Sludge as A Resource
- While sludge is essentially a waste product, there is increasing focus on its potential as a resource (i.e. sludge valorisation), specifically with reference to its: 1. latent energy (or calorific content, which can be used to quantify its potential for methane and/or hydrogen production), and 2. nutrient content (phosphate and nitrate). There is also significant interest in, and increasing i…