Wastewater And Climate Change

Wastewater refers to water that is used to carry municipal waste flows from domestic, commercial and industrial flows. It is largely an under-regarded and under-regulated area in relation to climate change.

However, mounting evidence shows that it is an important part of both climate change mitigation and adaptation, contributing to and being affected by the phenomenon.

Let us start with mitigation.

Only about 20% of water globally is treated, while the rest is discharged in its raw form vastly polluting the environment and releasing climate warming emissions. Wastewater contributes to 5% of worldwide emissions.

Wastewater uses a lot of energy in collection from source, transport and treatment of influent (incoming sewage). This energy is mostly electricity or vehicular transport of which the system is powered by fossil fuels which are the number one source of greenhouse gas emissions that cause climate change.

WWTP works at Ruai, Nairobi (Picture:Edison Mutumba)

When the waste has arrived at the central treatment place which is a wastewater treatment plant (WWTP), it is taken through various processes. One step is aeration, in which vast amounts of air are forced through the sludge. This process consumes energy. Also, the aim is to trigger aerobic decomposition (this requires oxygen) and the result of which is carbon dioxide which is a greenhouse gas.

Methane on the other hand is produced from anaerobic digestion, which occurs in the absence of oxygen. This happens when the sludge (solid matter) is either heated or decomposed in anaerobic digesters. Methane (CH4) is a strong GHG with a global warming potential of 25 over a hundred years. It is stronger than carbon dioxide in the short term. It is the main component of biogas released from waste.

In fact, emissions from WWTPs are mostly methane, which is also released from organic landfills and wherever waste (including hotel and kitchen waste) decomposes without oxygen. Both the treatment process of water and the sludge itself release the gas. Methane from wastewater tallies anywhere between 3- 19% of global CH4 emissions.

The positive side of this is that to reduce emissions, methane can be collected and used as an energy source. When burnt to produce energy, it is a little less harmful (CO2 released is little in volume). Sludge, when broken down in ideal conditions can provide significant amounts of methane-based energy such that the plant can be self-reliant in terms of energy sources and be independent of the main grid. In fact, the excess gas can be sold as a source of income for the plant and the facility becomes neutral in terms of carbon (because non-fossil fuel energy is used).  A WWTP is energy positive when it supplies back more power than used to the grid. This serves to reduce costs. This would cut reliance on fossil fuel energy and thereby GHG emissions because this methane is somewhat cleaner and cheaper than coal, oil or natural gas.

In fact, when harnessed in good proportions from areas that are densely populated, are all connected to proper drainage systems and are served by highly equipped and efficient waste processing plants, the amounts of gas produced can power even a city and go a veritably long way to cut emissions.

Another benefit is that the sludge when dried and disinfected can be sold as fertilizer to increase soil fertility in agricultural land, all this depending on regulatory regimes and social acceptability. This is a part of the circular economy.

Sludge is alternately landfilled or stored in lagoons.

Another greenhouse gas produced from wastewater is nitrous oxide (N2O), a part of the nitrogen cycle and derived from the action of nitrification and denitrification bacteria. Waste with a strong nitrogen-compounds component produces N20 of which about 3% of global totals is from wastewater.

Untreated waste water which is the vast majority is released back to the environment polluting land and poisoning water bodies. Such waterbodies are over fertilized and undergo eutrophication and harmful algal blooms which destroy marine life and later on release methane when the vegetation starts rotting. In fact untreated waste water is 3 times more harmful (in terms of emissions) for climate than treated water.

This untreated water poisons freshwater drinking sources for human consumption such as surface water (rivers, lakes, and springs) and ground water (aquifers).

The waste water sector is affected by climate change in various ways. Rising sea levels, increasing temperatures, heavy rains, flash floods and droughts all impact the sector.

Sea level rise first threatens to inundate wastewater plants located near the coast. These plants are normally located near discharge locations which for coastal communities is the sea. Secondly, the flow of treated waste water can be reversed when instead of flowing into the sea by gravity it is forced back into the plant by rising ocean water. This would require further pumping and other activities that require energy.

Saline water intrusion caused by encroaching seas can rapidly pollute freshwater aquifers (groundwater). The process also raises the water table inland and poses a big threat of contamination of groundwater as it mixes with waste from latrines, septic tanks and landfills. Such utilities are usually above groundwater but in a safe depth health-wise in the land so as to enable nutrient mixing in the soil. Sea level rise, storm surge and flash floods can also inundate lagoons or fields that store waste posing a huge threat to public health.

Droughts affects WWTPs in that they reduce the volume of water used to wash away solid waste. Because of water scarcity and as people conserve the resource more, this leads to accumulation of waste in the pipes and other infrastructure. The sludge begins to decompose and produces gases like hydrogen sulfide which erodes the pipes and degrades the infrastructure. This is costly for WWTPs.

Also, the concentration of pollutants and total dissolved solids (organic matter) goes up with less water available. The WWTPs lack flow of enough diluted water and so are overloaded in treatment capacity and unable to effectively remove all the harmful components and release treated and “safe” water that meets the required standards.

This requires WWTPs to adapt and adopt water reuse.

Droughts increase transpiration rates from water bodies and endanger water transport since there is not enough depth to support vessels. Some of these vessels carry waste from WWTPs.

Heavy rains causing excess floods on the other hand simply overwhelm the system. The wastewater system is flooded with more than it can handle and releases the excess back into the environment untreated. This is an immediate health hazard as sewage mixes with freshwater supplies and even the streets can be flooded with sewage. The risk is from excess phosphorus and high levels of bacteria and can easily initiate waterborne and dermatological diseases.

Strong storms caused by climate change directly destroy waste infrastructure and the storm surge floods buildings and cities. Seawater is corrosive and damages infrastructure. When there’s too much water, pumping is required which usually uses fossil fuel energy. Not only so, but climate caused migration stresses the limited capacity of wastewater facilities.

Rising atmospheric temperatures directly reduce water quality by catalyzing harmful algal blooms which makes water unsuitable for drinking and other uses. High temperatures thus increase the level of these and other organic contaminants and also promote the dissolution of chemicals and multiplication of pathogens. It also promotes faster decomposition of organic waste. All this increases the workload of WWTPs and reduces their efficiency. Not only so, but because it increases bacterial activity, there’s bio-corrosion of infrastructure.

Combined with droughts, heatwaves and hotter days increase water demand and induce water recycling in individual homes meaning less water for WWTPs.

Now, in light of all this, there’s some maneuvering space.

First, WWTPs help enhance groundwater flow by injecting reasonably treated water back into depleted or overexploited aquifers. However the water needs to be clean enough so as not to contaminate the aquifer with pollutants.

This method also stops to an extent saline intrusion by sea water along the coast.

When treated, waste water can be used for irrigation for farming, or for landscaping like lawns and golf courses. For this type of use, water needs to be sufficiently cleaned so that the crops don’t absorb the pollutants and in turn endanger human and animal health when they become part of the diet.

WWTPs can become a source of cooling water for power plants. The treated water can help reduce reliance by power plants on natural environmental flows. This will reduce competition with other water uses and also cut costs. The two can help each other.

The same water can be used in other industries as well.

Potable (drinking) water needs a higher level of treatment as the standards are higher for human consumption. If they can be met, then the water can be used where the laws and policies give the go ahead.

Water injection into aquifers need to be carefully balanced with other water recycling uses mentioned above, and with discharge back into natural water flows. Some ecosystems acting as a habitat for unique species are heavily reliant on downstream flow which requires adequate amounts of water. A lot of this is from the discharge of safe water from WWTPs. The same can be said of water based industries such as fisheries, tourism or recreation. They need adequate amounts of water.

Concerning WWTPs, some of the ways to deal with climate change can include the deployment of membrane technologies to treat waste water such as ultra or nano filtration or most commonly reverse osmosis which is used in desalination of seawater. RO however needs relatively clean feed water which increases costs of pretreatment chemicals (coagulants and flocculants) used to make pollutants coalesce and be easily removed beforehand.

Such efficiently clean water in order to reach the health standards of reuse.

WWTPs can use clean energy such as solar or wind energy which is climate safe in order to pump or collect sewage. They can also be more innovatively designed to enable maximum capture of gases and less power use.

All this requires the right regulation i.e. policy and laws. This is in turn determined by education and awareness among both the public and policymakers.

More research is required into this area involving all participants and stakeholders including the scientific community and academic institutions. This information should then be shared in an unfiltered manner.

Increased synergy and cooperation among all the players of the water sector is needed including water supply firms, water basin regulatory authorities, local government especially and community based organizations etc.

Better and round the clock monitoring of the wastewater sector, including on the supply side of water is needed to ensure efficient and smooth running of the system. This would need more skilled manpower and technical capacity.

Increased forecasting to predict climate change events, which helps in planning better and increases preparedness is necessary.

There is need for new ways to store recycled water. If storage solutions which are durable and have large capacity can be found, WWTPs can reduce the effect of droughts and associated climate phenomena on their operations.

More research into new and innovative technologies for wastewater sector. Technology is one of the positive things mankind has invented. Simple, easily imitable and transferable technology can help this sector deal with climate change.

This ties in with the need for durable materials for wastewater infrastructure. Such can withstand both extremes of too much or too little water, expansion or contraction due to temperature changes and the effects of biological organisms in waste.

Increased investment into this sector is needed. The first step is to recognize its importance and contributions to climate change.

Of course this means involvement of the sector in Nationally Determined Contributions and all other climate plans including adaptation plans of each country.