Comment: John Tattersall, Black & Veatch
Wastewater should be seen as a valued resource, says John Tattersall.
The Gulf Cooperation Council (GCC) states have the highest per-capita water consumption in the world, which is startling for such an arid region. As a result, there is growing recognition that current demand-supply balance trends are unsustainable.
A paradigm shift in how we view wastewater can contribute significantly towards sustainability. We need to think of wastewater treatment works as resource recovery plants. Utilities need partners with the technological understanding of, and experience in, wastewater recycling and unlocking wastewater’s potential as a source of renewable energy and nutrients.
By viewing water and wastewater holistically, rather separately, businesses can be made to create resources that can also fund growing infrastructure needs, as seen at Saudi Arabia’s National Water Company (NWC). Under Loay Al-Mussallam, NWC is switching its commercial focus from drinking water sales, which are heavily subsidised, to recycled water sales – mainly for industrial and government customers.
Advanced water treatment systems can recycle wastewater for basic and high-purity industrial applications, and irrigation. Although interest in reuse is growing, Abu Dhabi plans to recycle 100 per cent of its wastewater for irrigation by 2018, which currently represents a small proportion of overall supply - around 7 per cent. However, in Singapore, the country’s NEWater programme currently meets around 30 per cent of its needs.
Domestic wastewater streams are also excellent sources of renewable energy. Biogas produced during wastewater treatment can be processed to fuel combined heat and power (CHP) engines. At a time when GCC states are starting to reevaluate their energy consumption this may represent an attractive proposition.
The advanced sewage sludge digestion techniques required to maximise the benefits of biogas generation have been used extensively in the UK. Black & Veatch has been involved in several significant design-build generation projects; and recently commissioned the £105 million advanced sludge treatment facility at Davyhulme, Manchester. The process improves the digestibility of the sludge so the biogas yield is increased. The gas is used to generate electricity on site using CHP engines. The works is energy self-sufficient, and has the ability to export electricity to the grid. In the GCC, Taqa, Abu Dhabi’s National Energy Company, is among those investigating the use of biogas from wastewater as a fuel for electricity generation.
Nutrients are another resource we can recover from domestic wastewater. Phosphorus, vital for fertilisers required in food production, is a finite resource. Wastewater contains about 2.5g of phosphorus per person per day. Thus the wastewater treatment process offers the chance to recover this resource. At US’ Durham Advanced Wastewater Treatment Facility, nutrient recovery technology extracts 90 per cent of the phosphorus in the wastewater’s liquid stream, producing 500 tons of fertiliser annually.
In arid regions, like the Gulf, recognising that power and water are inextricably linked is crucial. Energy generation is water intensive and water services are energy intensive; reducing demand for one will reduce consumption of the other. This is even more important when customers in the GCC have some of the world’s highest per-capita demands for both. Meeting governments’ objectives will increasingly require experts in delivering both water and energy projects, and successfully combining insights from both.
Similarly, understanding generation technologies too has a significant impact. For example Saudi Arabia’s average thermal efficiency in generation is around 30 - 35 percent. Converting the kingdom’s single-cycle plants to combined-cycle is estimated to increase thermal efficiency to 40 - 45 percent. Combined cycle plants generate nearly 66 percent more energy per unit of water used compared to traditional gas fired plants. So, by understanding the technology and the nexus of water and energy, you begin to see a virtuous circle with more efficient generation coupled with a reduction in demand for water.
Air cooling, while impacting generation efficiency is another way to reduce power companies’ water requirements. Creation of a combined cycle power plant at Zarqa, Jordan, had to overcome scarce groundwater resources. To address this, the design called for cooling with a 16-cell, air-cooled condenser. In South Africa, Eskom’s 4,800 MW Kusile power plant will be one of the largest power plants in the world using air-cooling technology; saving approximately 327,000 cubic meters per day of water when operating at full load.
The announcement by Bahrain’s Minister of Electricity and Water that the GCC is commencing studies for a common regional water network is interesting. Geographic information system (GIS) technology can bring innovation to 21st Century transfer projects.
Despite the advances discussed, technology alone will not meet GCC states’ demand for water. It is observed around the world that helping people recognise water’s value is central to any sustainable demand management strategy.