Understanding Alkalinity Pollution: Causes And Impacts

Alkalinity is the capacity of water to resist acidification, or its ability to neutralise acids. It is a measure of how well water can resist changes in pH when acids are added. Alkalinity is crucial for maintaining stable conditions in natural bodies of water, as well as in aquariums and pools. It is also important for treating wastewater and drinking water. Alkalinity pollution can be caused by a variety of factors, including industrial effluents, agricultural runoff rich in fertilisers, and urbanisation.

Industrial effluents

The industrial sector, driven by processes like oil refining, excavating, tanning, pharmaceuticals, and pulp and paper production, generates substantial amounts of wastewater. This wastewater often contains a complex mixture of pollutants, such as heavy metals, oils, solvents, and chemicals. For instance, industries like leather processing release chromium (Cr) into the environment, while other heavy metals like lead, tin, tungsten, and arsenic are attributed to specific industries such as paints, ceramics, electronics, and more.

The discharge of these industrial effluents without proper treatment poses a significant environmental concern. These effluents can introduce toxic heavy metals into aquatic ecosystems, causing long-lasting pollution due to the metals' slow dissolution and disintegration. The presence of these metals and other pollutants in water bodies can have detrimental effects on aquatic life, including fish populations, and can also impact human health.

Additionally, industrial activities contribute to "legacy pollution," where contaminants are left in situ and are extremely challenging to remedy. The exponential increase in industrialization further exacerbates this issue, leading to the consumption of large areas of agricultural land and the degradation of soil quality. The preservation of water sources from these pollutants is a critical challenge faced by society, necessitating the development of various treatment technologies to address this complex issue.

To summarize, industrial effluents are liquid byproducts of various industries, containing a diverse array of chemical and biological pollutants. Their discharge into water bodies without adequate treatment results in water pollution, altered alkalinity levels, and adverse effects on aquatic ecosystems and human health. Addressing this issue requires stringent regulatory measures, improved waste management strategies, and the implementation of diverse treatment technologies.

Agricultural runoff

One significant contributor to agricultural runoff is animal waste from livestock farming, which contains high levels of nutrients, pathogens, and organic matter. When washed into water bodies, manure increases the biological oxygen demand (BOD), degrading water quality. Large-scale concentrated animal feeding operations (CAFOs) produce substantial amounts of waste, and inefficient waste storage and disposal can lead to spills and leaks, especially during heavy rains. This contaminates surface and groundwater with nutrients, bacteria, and other pollutants.

Agricultural practices involving fertilizers and pesticides also play a role in altering alkalinity levels. Fertilizers, including nitrogen-based, phosphorus-based, and potassium-based types, are essential for crop growth but can have detrimental effects when not properly managed. Excess nutrients from fertilizers contribute to eutrophication, promoting excessive algae growth and reducing oxygen levels in the water, leading to the creation of "dead zones" that cannot support most marine life.

Additionally, pesticides used in agriculture, such as insecticides, herbicides, and fungicides, can contaminate water bodies through runoff. Improper use or disposal of these chemicals can have unknown long-term health effects and negatively impact aquatic ecosystems. For example, the Great Barrier Reef has suffered from agricultural runoff containing pesticides and herbicides, disrupting the ecological balance and contributing to coral bleaching.

Poor land management practices, such as tilling, can also disrupt the soil structure, making it more susceptible to erosion. When soil is left bare and exposed, rainfall can easily dislodge soil particles, leading to sedimentation in rivers and streams. This sedimentation is a significant source of non-point source pollution, further degrading water quality. Deforestation and the removal of natural vegetation for agricultural expansion exacerbate soil erosion, highlighting the interconnectedness of agricultural practices and their impact on water alkalinity.

Urbanization

Additionally, the drilling of deep, large-capacity wells for industrial purposes can draw saltwater into drinking water wells and cause land subsidence, resulting in sinkholes. The construction of reservoirs to meet the water demands of growing urban populations can also alter stream channels, impacting the natural flow of water and the surrounding ecosystem.

To address these issues, strong city planning and management strategies are essential. This includes improving storm drainage systems, promoting wastewater reuse, and implementing measures to reduce air pollution, such as upgrading energy systems and encouraging alternative transport options.

Acid rain

The adverse effects of acid rain are widespread and detrimental. In natural ecosystems, acid rain contributes to soil acidification, stripping the soil of essential nutrients like calcium and magnesium, which are crucial for plant growth and healthy soil maintenance. This leads to a decline in forest health, with noticeable tree die-offs, particularly at higher elevations. The aquatic environment is also severely impacted, with many lakes, streams, and rivers unable to sustain healthy fish populations due to the disruption of their reproductive cycles. Acid rain also lowers the biological productivity of lakes and reduces the availability of forage fish for loons. Additionally, the acidification of water bodies causes metals, such as aluminium, to leach from the soil, altering the water chemistry and clogging fish gills, leading to the disappearance of aquatic species.

Beyond ecological impacts, acid rain has notable consequences for human infrastructure and health. It causes corrosion of steel structures like bridges, and the weathering of stone buildings and statues. Historical buildings and monuments are particularly vulnerable to the corrosive effects of acid deposition. Moreover, the pollutants that contribute to acid rain, such as SO2 and NO2, can form fine sulfate and nitrate particles that, when inhaled, pose risks to human health, including lung disease, heart attacks, and respiratory difficulties for individuals with asthma.

Recognising the severity of the issue, governments in Europe, North America, and other regions have implemented regulations to reduce sulfur dioxide and nitrogen oxide emissions since the 1970s. These efforts have been supported by scientific research and public awareness campaigns, leading to positive results in mitigating the harmful impacts of acid rain.

Anaerobic digestion

Alkalinity is a measure of how much acid water can neutralise. It is important in maintaining a healthy aquatic environment and ensuring safe drinking water. Alkalinity is usually measured in mEq/L (milliequivalent per litre) or, in the pool industry, in parts per million (ppm).

Alkalinity is closely related to the acid-neutralising capacity (ANC) of a solution. The acid-neutralising capacity refers to the combination of the solution and solids present (e.g. suspended matter, or aquifer solids). The alkalinity is equal to the stoichiometric sum of the bases in the solution.

In natural environments, carbonate alkalinity tends to make up most of the total alkalinity due to the common occurrence and dissolution of carbonate rocks and the presence of carbon dioxide in the atmosphere. Other common natural components that can contribute to alkalinity include borate, hydroxide, phosphate, silicate, nitrate, dissolved ammonia, the conjugate bases of some organic acids, and sulfide.

Alkalinity is influenced by runoff from soil, fallen leaves, and organic matter decomposition. Seasons also play a role; for example, increased rainfall can dilute these concentrations, thereby reducing the water body's total alkalinity. Pollution from industrial effluents, agricultural runoff rich in fertilisers, and urbanisation all contribute to altered alkalinity levels.

Alkalinity is significant in the treatment of wastewater and drinking water because it influences treatment processes such as anaerobic digestion. Alkalinity monitoring is crucial for stabilising pH and ensuring efficient biological processes.

A long-term anaerobic digestion process of the organic fraction of municipal solid wastes was performed and monitored, and alkalinity ratios were evaluated as effective indicators of process imbalances. Diverse stability limit values have been proposed in various works dealing with different substrates and experimental conditions. For example, an IA/PA ratio of 0.9 was suggested to maintain total VFAs below 2.5 g L-1 in thermophilic reactors treating sewage sludge, while an IA/PA ratio of 0.4 was proposed to assure stable reactor performance when treating potato-starch wastewater.

To determine reliable state parameters that could be used as early warning indicators of process failure due to the acidification of anaerobic digestion of food waste, three mesophilic anaerobic digesters of food waste with different operating conditions were investigated. Results revealed that operation conditions significantly affect the responses of parameters, and thus the optimal early warning indicators of each reactor differ from each other. A combination of total VFA, the ratio of VFA to total alkalinity (VFA/TA), and the ratio of bicarbonate alkalinity to total alkalinity (BA/TA) can reflect the metabolism of the digesting system.

Frequently asked questions