Sewage fungus [1] (also known as undesirable river biofilms, URBs) is a polymicrobial biofilm that proliferates in saprobic rivers [2] and has been frequently used as a bioindicator [3] [4] of organic river pollution for the past century. [5] Its presence has been strongly associated with discharges of untreated or inadequately treated sewage, [6] [7] [8] [9] yet its presence extends beyond these areas, with contributors including airport de-icers, [10] [11] [12] papermill effluents, [13] and agricultural runoff. [14] [15]
The name "sewage fungus" is somewhat of a misnomer, [5] as these growths are not primarily fungal in nature. Instead, they are complex polymicrobial biofilms bound within a matrix of extracellular polymeric substances. Taxa most frequently associated with sewage fungus include Sphaerotilus natans , Zoogloea spp., Beggiatoa alba , and Rhodoferax spp. [11] [16] [17]
In addition to being a bioindicator of organic pollution in rivers and playing a vital role utilizing excess organic carbon in fluvial systems, sewage fungus causes significant ecological impacts through direct and indirect ecological pathways.
Sewage fungus thrives in the low dissolved oxygen (DO) environment of an organically polluted river. [4] [17] [18] [19] Whilst DO is required for sewage fungus growth, it readily outcompetes other benthic organisms at low DO, [20] [21] [22] quickly smothering riverbeds, greatly altering the benthic habitat for invertebrates [23] [24] and fish spawning. [2] [25] [26] The dominating growth of sewage fungus also reduces hyporheic exchange flows, an important part of a rivers self-cleaning system. [27] [28] Similar river biofilms are also reported to accumulate heavy metals [29] [30] and other toxic substances. [31] within their matrix causing ecological impacts throughout the food web. [32] [33] As a heterotroph, sewage fungus uses considerably higher DO than an aquatic macrophyte of the same mass, [34] it can maintain DO concentrations below thresholds required for other organisms. Once sewage fungus becomes established, it is difficult to remove, [35] unless all sources of organic nutrients (pollution) are addressed, causing a further loss in biodiversity [36] and other flora and fauna [37] [38] in the river. These ecological impacts and the striking visible presence of sewage fungus growth on a riverbed further affects people's perceptions and use of rivers. [7] [39]
Sewage fungus is a polymicrobial biofilm and the specific composition of which is affected by the available nutrients (especially organic carbon sources) and the environmental drivers of each unique occurrence. However, several key taxa are reported as highly frequent and dominant within sewage fungus.
Sphaerotilus, and especially S. natans , has been strongly associated with sewage fungus since its inception [5] and continues to be regarded as a key sewage fungus taxon. [11] [12] Consequently, Sphaerotilus has been used seemingly synonymously with sewage fungus and a series of laboratory studies use S. natans as sewage fungus. [25] [40] [41]
Other key taxa include the bacteria Zoogloea spp., Beggiatoa spp., Thiothrix II , Flavobacterium spp. , and Flexibacter spp. . [16] [17] However, fungi (e.g., Leptomitus lacteus, Geotrichium candidum, and Fusarium aquaeductuum), algae (e.g., Cladophora glomerata) along with archaea and protozoa (e.g., Carchesium polypinum) also form integral and important pasts of the biofilm.
Recent genomic studies of sewage fungus composition have identified some of these taxa within airport de-icer implicated occurrences but have also identified new taxa not previously associated with sewage fungus. Exton et al (2023) identified Rhodoferax as a dominant component of sewage fungus, [11] whereas Nott et al (2020) noted the presence of Thiothrix. [12]
Alongside the complex nutrient utilisation requirements of sewage fungus, there are several key environmental drivers including substrate type, flow velocity, temperature, shading/sunlight, and water chemistry (e.g. pH).
Flowing water is a requirement for sewage fungus growth, to provide a constant replenishment of nutrients. [2] [4] [42] However, if the velocity of the river is too fast, then growths are scoured away, especially on more readily mobilised substrates. In turn, the specific flow of the river shapes the morphotype and structure of the biofilm. [43] Intrinsically the substrate affects the upper limit of flow as more stable riverbeds are less readily mobilised in periods of higher flows. Surfaces such as large cobbles, anthropogenic litter (e.g., bricks), and concrete channels facilitate excellent sewage fungus growth, whereas fine sediments and gravel provide a less stable substrate.
A biofilm is a syntrophic community of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymeric substances (EPSs). The cells within the biofilm produce the EPS components, which are typically a polymeric combination of extracellular polysaccharides, proteins, lipids and DNA. Because they have a three-dimensional structure and represent a community lifestyle for microorganisms, they have been metaphorically described as "cities for microbes".
Brine is water with a high-concentration solution of salt. In diverse contexts, brine may refer to the salt solutions ranging from about 3.5% up to about 26%. Brine forms naturally due to evaporation of ground saline water but it is also generated in the mining of sodium chloride. Brine is used for food processing and cooking, for de-icing of roads and other structures, and in a number of technological processes. It is also a by-product of many industrial processes, such as desalination, so it requires wastewater treatment for proper disposal or further utilization.
Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, including being safely returned to the environment. Water treatment removes contaminants and undesirable components, or reduces their concentration so that the water becomes fit for its desired end-use. This treatment is crucial to human health and allows humans to benefit from both drinking and irrigation use.
Water pollution is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water pollution results when contaminants mix with these water bodies. Contaminants can come from one of four main sources: sewage discharges, industrial activities, agricultural activities, and urban runoff including stormwater. Water pollution is either surface water pollution or groundwater pollution. This form of pollution can lead to many problems, such as the degradation of aquatic ecosystems or spreading water-borne diseases when people use polluted water for drinking or irrigation. Another problem is that water pollution reduces the ecosystem services that the water resource would otherwise provide.
Biochemical oxygen demand is an analytical parameter representing the amount of dissolved oxygen (DO) consumed by aerobic bacteria growing on the organic material present in a water sample at a specific temperature over a specific time period. The BOD value is most commonly expressed in milligrams of oxygen consumed per liter of sample during 5 days of incubation at 20 °C and is often used as a surrogate of the degree of organic water pollution.
Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, and microbiotic oxidation of contaminants in air. Industrial biofiltration can be classified as the process of utilizing biological oxidation to remove volatile organic compounds, odors, and hydrocarbons.
First flush is the initial surface runoff of a rainstorm. During this phase, water pollution entering storm drains in areas with high proportions of impervious surfaces is typically more concentrated compared to the remainder of the storm. Consequently, these high concentrations of urban runoff result in high levels of pollutants discharged from storm sewers to surface waters.
Aerobic granular reactors (AGR) or Aerobic granular sludge (AGS) are a community of microbial organisms, typically around 0.5-3mm in diameter, that remove carbon, nitrogen, phosphorus and other pollutants in a single sludge system. It can also be used for wastewater treatments. Aerobic granular sludge is composed of bacteria, protozoa and fungi,which allows oxygen to follow in and biologically oxidize organic pollutants. AGS is a type of wastewater treatment process for sewages and/or industrial waste treatment. AGR was first discovered by UK engineers, Edward Ardern and W.T. Lockett who were researching better ways for sewage disposal. Another scientist by the name of Dr. Gilbert Fowler, who was at the University of Manchester working on an experiment based on aeration of sewage in a bottle coated with algae. Eventually, all three scientists were able to collaborate with one another to discover AGR/AGS.
Heterotrophic picoplankton is the fraction of plankton composed by cells between 0.2 and 2 μm that do not perform photosynthesis. They form an important component of many biogeochemical cycles.
The class Flavobacteriia is composed of a single class of environmental bacteria. It contains the family Flavobacteriaceae, which is the largest family in the phylum Bacteroidota. This class is widely distributed in soil, fresh, and seawater habitats. The name is often spelt Flavobacteria, but was officially named Flavobacteriia in 2012.
Pepper mild mottle virus (PMMoV) is a plant pathogenic virus that occurs worldwide on species of field grown bell, hot and ornamental pepper species. It is caused by members of the plant virus genus Tobamovirus—otherwise known as the tobacco mosaic virus family. Tobamovirus are viruses that contain positive sense RNA genomes that infect plants. Symptoms of the disease vary depending on the cultivar. Typical symptoms include the chlorosis of leaves, stunting, and distorted and lumpy fruiting structures. The virus is spread by mechanical transmission and infected seeds. Avoidance is the best means of controlling the disease because once a plant is infected it cannot be treated. Only seeds that have been tested and treated for the pathogen should be planted.
Extracellular polymeric substances (EPSs) are natural polymers of high molecular weight secreted by microorganisms into their environment. EPSs establish the functional and structural integrity of biofilms, and are considered the fundamental component that determines the physicochemical properties of a biofilm. EPS in the matrix of biofilms provides compositional support and protection of microbial communities from the harsh environments. Components of EPS can be of different classes of polysaccharides, lipids, nucleic acids, proteins, lipopolysaccharides, and minerals.
Water pollution is a major environmental issue in India. The largest source of water pollution in India is untreated sewage. Other sources of pollution include agricultural runoff and unregulated small-scale industry. Most rivers, lakes and surface water in India are polluted due to industries, untreated sewage and solid wastes. Although the average annual precipitation in India is about 4000 billion cubic metres, only about 1122 billion cubic metres of water resources are available for utilization due to lack of infrastructure. Much of this water is unsafe, because pollution degrades water quality. Water pollution severely limits the amount of water available to Indian consumers, its industry and its agriculture.
Pollution-induced community tolerance (PICT) is an approach to measuring the response of pollution-induced selective pressures on a community. It is an eco-toxicological tool that approaches community tolerance to pollution from a holistic standpoint. Community Tolerance can increase in one of three ways: physical adaptations or phenotypic plasticity, selection of favorable genotypes, and the replacement of sensitive species by tolerant species in a community.
Sphaerotilus natans is an aquatic periphyton organism associated with polluted water. It forms colonies commonly known as "sewage fungus", but later identified as tightly sheathed filamentous bacteria.
The plastisphere consists of ecosystems that have evolved to live in human-made plastic environments. All plastic accumulated in marine ecosystems serves as a habitat for various types of microorganisms, with the most notable contaminant being microplastics. There are an estimate of about 51 trillion microplastics floating in the oceans. Relating to the plastisphere, over 1,000 different species of microbes are able to inhabit just one of these 5mm pieces of plastic.
Moving bed biofilm reactor (MBBR) is a type of wastewater treatment process that was first invented by Professor Hallvard Ødegaard at Norwegian University of Science and Technology in the late 1980s. The process takes place in an aeration tank with plastic carriers that a biofilm can grow on. The compact size and cheap wastewater treatment costs offers many advantages for the system. The main objective of using MBBR being water reuse and nutrient removal or recovery. In theory, wastewater will be no longer considered waste, it can be considered a resource.
Bioclogging or biological clogging refers to the blockage of pore space in soil by microbial biomass, including active cells and their byproducts such as extracellular polymeric substance (EPS). The microbial biomass obstructs pore spaces, creating an impermeable layer in the soil and significantly reducing water infiltration rates.
Jennifer Lee Stauber is an Australian ecotoxicologist and chief research scientist at the CSIRO Land and Water.
Phytobenthos (from Greek φυτόν and βένθος are autotrophic organisms found attached to bottom surfaces aquatic environments, such as rocks, sediments, or even other organisms. This photosynthetic community includes single-celled or filamentous cyanobacteria, microalgae, and macrophytes. Phytobenthos are highly diverse, and can be found in freshwater and marine environments, as well as transitional water systems. However, their distribution and availability still depend on the factors and stressors that exist in the environment. Because phytobenthos are autotrophs, they need to be able to subsist where it is still possible to perform photosynthesis. Similar to phytoplankton, phytobenthos contribute to the aquatic food web for grazers and heterotrophic bacteria, and researchers have also been studying their health as an indicator for water quality and environmental integrity of aquatic ecosystems.
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