Optimising wastewater treatment through measurement

How digital measurement is helping to maximise wastewater treatment efficiency.

Water is vital for life, yet despite 70% of the Earth’s surface being covered in water, limited quantities are available to sustain humanity. The 97% of water retained in the world’s oceans is too salty to drink or use for growing crops. Only 3% of the Earth’s water is fresh, and the majority of that water is held in ice caps and glaciers.

The remaining small percentage must meet all the potable drinking water and agricultural needs of a planet with a rapidly expanding population. Given this, it is not surprising that water scarcity is a growing issue across the globe, affecting every continent. Water scarcity can be caused by a physical shortage, the failure of institutions to produce and provide a regular supply, or a lack of infrastructure to distribute water.

Water scarcity in numbers

The scale of the problem is summed up by some sobering figures. Approximately four billion people — half of the world’s population — experience severe water scarcity for at least one month each year, while over two billion people live in countries with an inadequate water supply.

This lack of water could have profound social consequences, with 700 million people potentially being displaced by intense water scarcity by 2030. Lack of water also disproportionately affects women and children — spending time fetching water from great distances means they cannot fulfil their education or employment prospects. It has been estimated that by 2040, around 25% of the world’s children will be living in areas suffering from extremely high water stress.¹

Preserving water supplies

One of the key aspects of water supply is preserving existing sources and safeguarding them against pollution. A key source is groundwater, which is found in aquifers, formations of rocks, sand and gravel that hold substantial quantities of water. Accounting for approximately 99% of all liquid freshwater², it feeds springs, rivers, lakes and wetlands. Once regenerated from rain and snowfall infiltrating the ground, it can be extracted to the surface for use by pumps and wells.

In arid areas without rivers and lakes, groundwater is usually the only source. Even in relatively wet areas, groundwater aquifers remain an important source of water for drinking, sanitation, agriculture and industry. Almost all the liquid freshwater in the world is groundwater, and around 40% of all water used for crop irrigation comes from aquifers.

Some countries are putting their groundwater sources under growing stress, with Asia and the Pacific region having the lowest per capita water availability in the world. The use of groundwater in the region is predicted to rise by 30% by 2050.

Conserving and preserving supplies of groundwater is therefore vital in ensuring a sustainable water supply that meets both the demands of current and future generations. As a way of recovering and restoring supplies of used water, wastewater treatment processes have a key role to play in achieving this, making accurate and reliable measurement a key requirement.

Figure 1: Countries at most risk of water crisis. For a larger image click here.

Global trends affecting water use

Several global trends are having a major impact on how water is treated and distributed, its availability and how it is used.

Urbanisation and development

Recent years have seen a major trend of mass migration to cities as people seek a higher quality of life. For the first time in human history, over half of the world’s population lives in towns and cities, a proportion that is set to rise to two-thirds by 2050. Less-developed regions are seeing the fastest population growth in urban areas, with the urban population estimated to grow from 3.9 billion people today to 6.3 billion in 2050.³

As well as increasing wastewater quantities, increased urbanisation also expands the range of potential pollutants that need to be treated. This requires an increased range of measurements to detect them and make sure they are either removed or reduced to safe limits.

Industrialisation

The growth in urban populations has seen a corresponding increase in industrialisation, as people demand more consumer and household goods. This brings consequences for water supplies, both in the increased use of water for manufacturing and the toxic chemicals that can enter the water supply.

Many industrial units discharge wastewater locally without treatment or as waste into lakes, rivers and oceans. These can include pesticides, chemicals, waste oils and heavy metals, which can be accumulated by humans and other living organisms in their tissues. Untreated sewage discharged into rivers can cause diseases like typhoid, dysentery and cholera, while plant supplements like nitrate and phosphates can stimulate the growth of algae.

Agriculture

Agriculture looks set to remain the biggest user of water, with demand for new foodstuffs and products keeping water use high.

Agriculture is a major source of water pollution. Chemicals such as nitrogen and ammonia from fertilisers frequently enter watercourses as surface run-off from fields. Once present in water these chemicals can cause significant damage, killing aquatic life and accelerating the growth of vegetation such as algae. If the chemicals are left uncontrolled, eutrophication and other problems may occur.

Climate change

As the climate changes, the availability of water is becoming less predictable. One of the growing threats is flooding, which can destroy water points and sanitation facilities, and contaminate water sources. Some regions are experiencing droughts that increase water scarcity and reduce people’s health and productivity. Continued access to water is one of the major strategies as we seek to mitigate the effects of climate change.

Other effects, such as increased temperatures and more extreme, less predictable weather, may alter the patterns of rainfall and snowmelt. This can disrupt or alter river flows and groundwater, further reducing the available quantities of water.

All this puts an onus on ensuring wastewater flows can be recovered and returned to high-quality supplies of potable water with as little treatment as possible.

Decarbonisation

The production, distribution and treatment of water is highly energy-intensive and contributes to a nation’s carbon production. For example, in the UK, carbon emissions from domestic and non-domestic supplies by water companies are 5.03 MtCO2e. This rises to 35 MtCO2e when household water use is factored in.⁴

Many water companies have signed up to become carbon neutral, but turning wastewater into a suitable state for discharge into watercourses such as streams, rivers and the sea can be an energy-intensive process. Accurate measurement to ensure close control of treatment processes is therefore a key requirement to help limit energy consumption.

Why does measurement matter for wastewater treatment?

Wastewater treatment is a multi-stage process that involves a wide range of measurements needed to make sure that both the quality and quantity of discharged water meet increasingly strict regulatory requirements.

The process of bringing wastewater flows back to an appropriate condition, fit for discharge, requires knowledge of the condition of that water as it travels from the treatment plant input to the point of final discharge, much like a journey begins with knowing your destination.

Consequently, there is a wide range of parameters that need to be accurately measured at each point in the wastewater treatment cycle. While previous measurement techniques have varied in their accuracy and effectiveness, the latest generation of digital continuous instruments and analysers is helping to transform measurement performance. Collecting and transmitting a range of operational and diagnostic data, these devices offer the opportunity to get a clearer indication of process conditions that can be used to optimise treatment performance and demonstrate regulatory compliance.

Environmental advantages

Regulations designed to protect the environment encompass everything, from tackling the spread of invasive species to minimising chemical and nutrient pollution. Returning high-quality water to the water cycle ultimately provides maximum availability when utilities withdraw water.

But the treatment and distribution of water are also energy-intensive: an important aspect of protecting the environment is optimising processes and cutting carbon emissions in the treatment and distribution cycle.

Digital measurement and analysis of the wealth of data provided helps to assess current performance and identify ways that it can be improved to help companies minimise their environmental impact and comply with relevant rules and regulations.

Operational advantages

Digitalisation gives a better overview of processes, enabling decisions to be made on a more informed, objective basis. Systems running analytical programs provide insights into key operations such as pH measurement and control. This analysis offers the ability to anticipate changing process trends, deal with potential anomalous conditions as they occur and help the organisation achieve higher-level operational and business objectives.

Maximising the value of the data is increasingly enabled by advances in artificial intelligence and machine learning. Multiple streams of data are collected and analysed to establish patterns of behaviour and trends, and these patterns and trends predict future outcomes, allowing utilities to operate more efficiently.

Online measurement is the most common type of measurement used by water companies today. Extractive sampling and testing onsite, which were once frequently employed to determine the quality of the water, are now mostly used to check that onsite continuous water analysis systems are producing accurate results.

One of the great advantages of online continuous water analysis is the ability to respond quickly to changing conditions. This has delivered large-scale efficiencies for water treatment works by enabling them to identify processes that may not be performing at their optimum and take necessary measures to address any problems.

Digital measurement and sensing equipment, together with advanced data processing techniques and increasingly capable computers, are creating what is effectively a ‘digital brain’. As utility companies have upgraded instruments and systems over time, there has been scaled investment in the infrastructure to maximise the value of the data.

It is not only tightening environmental legislation that motivates the use of continuous water analysers. At the most basic level, plant managers implement digitalisation to improve their snapshot view and gain an understanding of what’s happening in their current operations. At the highest levels, the data is used strategically for improving customer satisfaction, balancing the allocation of capital and supporting better decision-making in day-to-day business, financial and operational activities.

With digital instrumentation being used to measure an extensive range of parameters from dissolved oxygen in the aeration process to chlorine and turbidity, continuous water analysers help to eliminate the delays and added uncertainties associated with extractive testing methods.

Figure 2: Energy burden in sewage treatment. For a larger image click here.

Cost

Wastewater treatment is an expensive process. Huge amounts of energy are needed to shift water between the various stages as well as treating water in processes such as aeration, which can often account for over 50% of a typical site’s total energy burden.

Another significant cost is that of chemical consumption. Many of the processes in wastewater treatment consume chemicals, either directly through dosing or indirectly for purposes such as producing the chemical reactions in measurement instruments needed to assess water quality. Using instruments that can measure to the highest levels of accuracy is therefore key to reducing the risk of errors that might require costly retreatment of wastewater flows. By enabling problems to be quickly spotted, the latest generation of measurement instruments and analysers allows timely action to be taken before any problems can escalate.

Maintenance

Water treatment works in isolated and difficult-to-reach locations are expensive to routinely maintain. As the front line in any water quality measurement scheme, continuous water quality analysers need to be kept in good working order to provide accurate, reliable and repeatable performance. In these instances, predictive maintenance allows maintenance workers to schedule their work to make sure sensors are functioning properly. Combining preventive maintenance and predictive maintenance helps maximise process efficiency and guarantee that everything is operating as it should.

Digital sensors and transmitters are offering additional data above and beyond their primary measurement that indicates instrument health. If readings are not as expected, digital instruments can feedback advanced self-diagnostics conforming to NAMUR NE107.

Figure 3: Why measurement matters. For a larger image click here.

Conclusion

With projections estimating that the world’s population will continue to grow to 9.8 billion people by 2050, every possible effort must be made so that every drop of water can be conserved and preserved to meet growing demand.

Maximising the efficiency of wastewater treatment processes can help to reduce the risk of pollution of the ground and surface water sources that supply raw water for potable treatment. By taking advantage of the many benefits of the latest generation of digital measurement technologies, operators can be sure that the quality of the water they discharge back to the environment meets the highest levels of quality and safety, while also finding ways to reduce costs and avoid the risk of regulatory infringements that could result in stiff financial penalties.

^{1. Unicef, Water scarcity: addressing the growing lack of available water to meet children’s needs, <<https://www.unicef.org/wash/water-scarcity>>}

^{2. United Nations 2022, ‘Groundwater: Making the invisible visible’, UN World Water Development Report 2022, <<https://www.unwater.org/publications/un-world-water-development-report-2022>>}

^{3. UN Water, Water and Urbanization, <<https://www.unwater.org/water-facts/water-and-urbanization>>}

^{4. UK Environment Agency, Greenhouse gas emissions of water supply and demand management options, <<https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/291728/scho0708bofv-e-e.pdf>>}

This article is based on an ABB white paper on wastewater treatment. Click here to read the full white paper.

Top image: iStock.com/abadonian