Sources Of Municipal Water Pollution: Understanding The Origins

Water pollution is the contamination of water bodies, which has a negative impact on their use. Water pollution is usually a result of human activities. Municipal water pollution is caused by sewage discharges, industrial activities, agricultural activities, and urban runoff including stormwater. Sources of water pollution are either point sources or non-point sources. Point sources are pipes or channels, such as those used for discharge from an industrial facility or a city sewerage system. Non-point sources are broad unconfined areas from which a variety of pollutants enter the water body, such as the runoff from an agricultural area.

Sewage and wastewater treatment

The treatment of sewage falls under the field of sanitation and aims to remove contaminants from sewage, producing an effluent that can be safely discharged into the environment or reused. This process is known as sewage treatment or wastewater treatment, and it plays a crucial role in preventing water pollution.

There are two main types of sewage collection systems: decentralized systems and centralized systems. Decentralized systems treat sewage close to where it is created, such as through on-site sewage facilities or septic tanks. On the other hand, centralized systems collect sewage through a network of pipes and pump stations and transport it to a municipal treatment plant. Centralized systems are further classified into sanitary sewers and storm sewers. Sanitary sewers carry only sewage, while storm sewers carry urban runoff or stormwater.

Sewage treatment typically involves primary and secondary treatment stages, with advanced treatment incorporating a tertiary stage. During primary treatment, about 60% of suspended solids are removed from wastewater, and the wastewater is aerated to restore oxygen levels. Secondary treatment removes more than 90% of suspended solids. Tertiary treatment, also known as advanced treatment, includes polishing processes and nutrient removal.

Wastewater treatment plants employ various technologies, ranging from high-tech, intensive systems to low-tech, extensive, nature-based systems. These processes are designed to reduce pollutants in wastewater to a level that nature can handle before it is released back into the environment. The treatment of sewage and wastewater is a critical aspect of water pollution prevention, ensuring that our water resources remain safe and sustainable for human use and healthy aquatic ecosystems.

Industrial activities

One of the main ways industrial activities pollute water is through improper waste disposal. Many industrial sites produce waste that contains toxic chemicals and pollutants, and if not properly managed or treated, this waste can easily contaminate nearby water sources. This can happen through direct dumping into freshwater systems or indirectly through runoff or seepage into the ground, which then contaminates groundwater.

Another issue is the discharge of partially treated or untreated wastewater into municipal sewer systems. Some industries install pre-treatment systems to remove some pollutants before discharging the water. However, the treatment may be inadequate, or the system may become overwhelmed, resulting in the release of contaminated water into waterways.

The types of pollutants released by industrial activities vary but often include heavy metals, volatile organic compounds, oil, grease, and nutrients such as ammonia. These pollutants can have severe ecological consequences, as they are toxic to aquatic life, reducing their lifespan and ability to reproduce. They can also disrupt entire ecosystems and have negative effects on human health, causing waterborne diseases such as cholera, giardia, and typhoid.

Furthermore, industrial activities contribute to water pollution through transboundary pollution, where contaminated water from one region or country spills into the waters of another. This can occur due to disasters, such as oil spills, or the gradual downstream creep of industrial emissions. Industrial sites located near bodies of water are particularly susceptible to this type of pollution, as contaminants can easily enter and accumulate in these environments.

To mitigate the impact of industrial activities on municipal water pollution, proper waste management and treatment systems are essential. While regulations exist, better enforcement and the development of alternative energy sources are crucial to reducing the release of toxic substances into our water systems.

Agricultural activities

Agriculture is a major contributor to water pollution. It is the single largest contributor of non-point-source pollution to surface water and groundwater, accounting for 70% of total water consumption worldwide.

Large-scale industrial farming, including livestock and fisheries, is categorized as point-source pollution, while small-scale family-sized farming is considered non-point-source pollution. Point-source pollution refers to contaminants that enter a waterway from a single, identifiable source, such as a pipe or ditch. Examples include discharges from sewage treatment plants, factories, or city storm drains. In contrast, non-point-source pollution comes from a broad unconfined area, like the runoff from an agricultural area, and is more challenging to control.

The use of antibiotics, fungicides, and anti-fouling agents in agriculture has increased, potentially contributing to polluting downstream ecosystems. Additionally, nitrate from agriculture is now the most common chemical contaminant in groundwater aquifers. Fish excreta and uneaten feeds from fed aquaculture also reduce water quality.

Agricultural pollution has been identified as the main factor in the degradation of inland and coastal waters in most high-income countries and many emerging economies, surpassing contamination from settlements and industries. The expansion of irrigation practices, the rise in livestock numbers, and the significant growth of aquaculture have all contributed to this.

Urban runoff

The sources of urban runoff pollution are diverse and can be challenging to control. One major source is atmospheric deposition, which includes pollutants from the air that are deposited onto surfaces and then washed away by rainwater. Another significant contributor is vehicular transportation-related activities, where pollutants from vehicles are released into the environment and can be carried by runoff water. In addition, metallic building envelopes have been identified as a source of pollution, releasing metals into the water supply.

The pollutants carried by urban runoff can include a range of contaminants, such as oil, grease, pesticides, herbicides, soil, pet waste, and more. These substances can have detrimental effects on aquatic ecosystems, reducing oxygen levels in the water and leading to the creation of "dead zones" where aquatic life cannot survive. The pollutants can also impact human health, as people may unknowingly use polluted water for drinking or irrigation, spreading water-borne diseases.

To address the issue of urban runoff, comprehensive strategies are necessary. The Water Quality Protection Program (WQPP) in the United States, for example, works with cities and counties to develop solutions through the Municipal Separate Storm Sewer System (MS4) permits. Additionally, educational efforts play a crucial role, as they help individual citizens understand their impact on water quality and make informed decisions to minimise their contribution to urban runoff. Implementing guidelines, such as the California Environmental Quality Act (CEQA), can also provide a framework for managing and reducing urban runoff pollution.

Poor sanitation

Water-borne diseases, infections, and pathogens are spread through contaminated water, causing severe health issues and even death in vulnerable individuals, such as the very young and elderly. These diseases include cholera, diarrhoea, dysentery, typhoid, and polio. Diarrhoea is the second-leading cause of death in children under five and is largely preventable by improving access to clean water, sanitation, and hygiene practices. According to the World Health Organization (WHO), improving access to these basic necessities could save 1.4 million lives per year.

Open defecation, a practice resulting from a lack of access to proper sanitation facilities, is a significant contributor to water pollution. During rain events or floods, human faeces deposited on the ground are washed into surface waters, contaminating them. This contaminated water then becomes a source of various diseases when consumed or used by people for other purposes. Simple pit latrines, which are a common solution in some areas, are also susceptible to flooding during heavy rainfall, leading to the same issue of water contamination.

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