Energy efficiency influencing water developments

11th October 2013

By: Carina Borralho

  

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These days there is a high awareness of energy efficiency in society, which is influencing new developments and upgrades in water technology, says South African research funder the Water Research Commission (WRC).

“Greater emphasis is being placed on using energy efficient equipment, such as pumps and air blowers. Should energy generation be required, miniturbines and biogas are often installed at a project,” says WRC project independent consultant Sue Freese.

The WRC tells Engineering News that it presented these findings of the South African Energy Compendium of Good Practice in Water and Wastewater at the fourth Municipal Water Quality Conference, at Sun City, in the North West, in July.

WRC scientist of water and wastewater quality Dr Marlene van der Merwe Botha says the discussions and presentations at the conference, hosted by the Department of Water Affairs (DWA) in partnership with the Water Institute of Southern Africa (WISA), showed the value and application of energy in the reticulation and treatment process of water and sewage.

“It is relevant to note that the recent assessments included energy as a criteria during water audits,” she adds.

Van der Merwe Botha explains that the South African Energy Compendium of Good Practice in Water and Wastewater is part of a Global Water Research Coalition (GWRC) project titled Energy Efficiency in the Water Industry: A Compendium of Best Practices and Case Studies.

The WRC embarked on the project, which documents global best practices in the water and wastewater industry, to position the water sector globally with regard to energy-consumption good practice.

The project is supported by the GWRC’s partners, represented by the four continental coordinators in Australasia (Australia and Singapore), Europe, South Africa and the US. Each continental group has produced a report covering examples of best practice submitted by utilities in its region. When all four continental reports are available, they will be compiled into the global compendium.

The WRC notes that the US and the UK reports are already available and the South African report is available from the WRC, while the Australasian report will be available in the next few months. “The global report will be available in 2014,” says Van der Merwe Botha.

Conference Outcomes

The WRC says conferences provide the opportunity to discuss new approaches and technologies for water and waste- water management as well as reflect and evaluate the successes or shortcomings of previously implemented approaches and initiatives.

A comprehensive background presentation by the GWRC at the fourth Municipal Water Quality Conference illustrated the water-energy nexus internationally and locally. “This introduction set the foundation and assisted the audience in conceptualising the current energy scenario,” says Van der Merwe Botha, adding that recent changes in State-owned power utility Eskom’s levies and direct costs to munici- palities were also discussed.

The conference successfully raised the issue of energy as a critical risk in the future of water and wastewater pumping and treatment, stimulating debate with regard to putting the most appropriate and sustainable control measures in place to prepare for higher energy costs in future.

Some municipalities have started with energy-focused projects, notes Van der Merwe Botha, but do not have a frame- work for the type of data that needs to be monitored as part of these projects. “These municipalities confirmed that the South African compendium assisted them in this regard,” says Van der Merwe Botha.

Further, it became apparent at the conference that many municipalities do not have the capacity to write business plans to approach Eskom for the green funding needed to conduct energy studies and projects, “although, they did express interest in pursuing some of the options presented during the workshop”, says Van der Merwe Botha.

Another aspect of the compendium that stimulated discussion was identifying the municipalities and plants where the case studies had been compiled, as this enables municipalities to engage directly with the case study project managers.

Van der Merwe Botha says it was also noted that the compendium presented positive results, which ultimately reflected positively on the sector and its members. “There were issues that arose during the compendium, but solutions to these were discussed,” she says.

Consequences of Power Outages

The WRC tasked consultant Frost & Sullivan with a project to help understand the poten- tial impact that current energy supply challenges are having on South Africa’s water and wastewater services, says Van der Merwe Botha.

She explains that the aim of this project is to provide the WRC and other stakeholders in the South African water and waste- water treatment sectors with an objective and logical evaluation of the current and expected impact of power outages on water and wastewater treatment services.

Frost & Sullivan has found that power outages directly impact on water and wastewater service delivery in South Africa. “Only a handful of cases that exposed distinct economic, environmental, social and health costs have been highlighted in this project, but there are certainly other similar cases,” adds Van der Merwe Botha.

Unless the power sector can guarantee that power outages are a thing of the past, the WRC says water decision-makers and managers will need to take appropriate steps to mitigate the impacts highlighted in the report or at least reduce them. “Failure to do so will result in costly economic, environmental, social and health consequences. It is also for this reason that the DWA regards energy as a risk of particular significance in water safety planning and wastewater risk abatement planning,” says Van der Merwe Botha.

WRC research manager Dr Jo Burgess says, contrary to the UK and US Energy Compendia, South Africa has not been actively pursuing and implementing energy savings projects on a large scale, mainly as result of the abundance of readily available and historically cheap electricity in the country.

South African Mindset

“Owing to recent droughts and water shortages, considerably more attention is now paid to the conservation of water and water demand management. However, a lot still needs to be done to change the mindset of the large portion of the population that believes water is abundantly available in South Africa,” says Van der Merwe Botha.

The WRC says, unfortunately, water loss of 25.4% through municipal supply systems indicates that water conservation needs to be prioritised if South Africa is to sustain an accept- able level of water security.

“The recently announced No Drop system follows the same model as the Green Drop and Blue Drop systems in aiming to incentivise water-use efficiency in municipalities,” notes Van der Merwe Botha, adding that, if it follows the same success curve as the other systems, it will take South Africa a long way towards meeting targets in water-loss reduction.

Case studies and operational data are not readily available and, in cases where energy savings applications have been implemented, the data is poorly recorded and not verified.

Freese highlights that there are some examples of initiatives in South Africa that are aimed at water conservation. “One successful initiative is the advanced pressure management system that was implemented in Durban in 2009, which reduced water losses in the area by 18.7 Mℓ/d,” she says, adding that this represents a significant cost saving.

An additional cost-saving benefit of this management system has been a consider- able decrease in burst pipes in Durban. Water conservation initiatives such as these impact on the amount of energy used in maintaining adequate water and wastewater service delivery.

Complex Water Supply Chain

“South Africa has one of the most advanced water and wastewater sectors in Africa. Understanding the complexity of South Africa’s water supply chain is a critical component of analysing the impact of power outages on this sector,” says WRC research manager Dr Valerie Naidoo.

“South Africa represents an interesting mix of First and Third World characteristics, which is also reflected in the multiple options of water and sanitation systems and technologies, which range from the basic to the highly sophisticated,” says Van der Merwe Botha.

The WRC points out that focus should be placed on the value of integrated planning across the various planning spheres, which demands strong human resource capabilities.

An example is the rate of housing development projects surpassing the rate of water supply, which has created several backlogs. “This places considerable pressure on existing water sources and demon- strates how individual elements in the cycle can trigger an entire cause-and-effect cycle,” adds Van der Merwe Botha.

Numerous factors influence the amount of energy used in the water supply chain, including the stage of the water supply chain, the technology used, the use of pump or gravity feeds and the quality of the water being treated.

The WRC notes that certain treatment technologies con- sume more energy than others – using reverse osmosis membranes, for example, consumes significantly more energy than other filtration techniques.

“Up to 50% in energy savings has been demonstrated in wastewater processes focused on aera- tion. Simple changes in control methods and set points have frequently shown substantial quick wins, and checks at plants and on control methods and operational routines where maintenance is concerned have also proved to be worthwhile,” says Freese.

She notes that off-peak pumping is another management tool that can enable significant reductions in energy use, but for large systems, which are extensive and complex, such as the one used in the greater Durban area, complicated programming and skilled personnel are necessary if the full potential energy saving is to be realised.

Case Study Findings

Van der Merwe Botha notes that reverse osmosis is used to desalinate water containing high salt concentrations, such as brackish groundwater or seawater. Desalination is applied only when there is no freshwater source available. Other desalination technologies include distilla- tion, which is commonly used in the Middle East and is equally, if not more, energy intensive.

“Aeration is required for any aerobic biological treatment process to convert wastewater into harmless end-products of water and carbon dioxide. Pond systems do not require the mechanically induced aeration of water, as this process takes place naturally. “This form of aeration, however, is suit- able only for low flows present in the wastewater treatment of small towns. Larger towns need mechanically induced aeration, which requires energy inputs,” adds Van der Merwe Botha.

Energy-Recovery Technologies

Van der Merwe Botha says the energy efficiency of existing operations can be improved by undertaking initiatives or implementing management systems that focus on, for example, pressure management in municipal water distribution systems, leakage reduction and water conservation, while other measures include off-peak pumping, solar heating, composting, digester- mixing optimisation for energy efficiency, energy-recovery devices in desalination systems, aeration at wastewater treatment plants, fine-bubble diffused air systems, vertical mixers for anaerobic digesters, diffused air injection (vertically aligned diffuser pipes), submersible versus self- priming pumps, pump efficiencies and water demand management, as well as energy efficiency management systems.

She further notes that the conversion of biogas into electricity and hydropower generation with mini hydroturbines in pressurised distribution can lead to energy generation in the water and wastewater sector.

A WRC survey, conducted in 2009 on the quality and quantity of wastewater in South Africa, identified the top three sectors with the greatest energy-recovery potential as the formal and informal animal husbandry, the fruit and beverage industries and domestic backwater.

“I believe this is still applicable. The strength and character of the substrate determine the energy potential, which defines these particular streams, among others,” says Van der Merwe Botha.

The WRC says, through hydrogeneration, an estimated 10 000 MWh can be recovered from wastewater in the whole of South Africa, representing 7% of the Eskom electricity supply.

“Energy has also become a key driver in the wastewater-treatment value chain of the City of Johannesburg and every effort is being made to produce green energy and reduce power consumption,” adds the WRC.

“Water utility Johannesburg Water is implementing the anaerobic digestion of sludge using cell lysis, scrubbing and primer technologies to increase conven- tional biogas (methane) production by 30%, thereby supplementing the energy demand of treatment plants by between 60% and 100%,” says Van der Merwe Botha, adding that the combined heat and power process can produce 10.2 MW of electricity and 12.2 MW of heat from five wastewater treatment plants that, in turn, enable the production of more than one-million cubic metres of water a day.

Johannesburg Water operates and maintains six wastewater treatment works, with about 1.054-million cubic metres of sewage treated a day in 2010. The activated sludge process was used to treat the sewage and about 90% of the 260 t of dry sludge produced a day consisted of waste-activated sludge.

The WRC estimates that, by 2020, the cost of electricity for the treatment of wastewater in Johannesburg will rise from the current R97-million a year to more than R300-million a year, possibly making the existing wastewater treatment operations in South Africa unaffordable.

It notes that the failure of the wastewater treatment operations will have a devastating effect on the economy, the environment, health services and social activities of the City of Johannesburg.

The Department of Energy’s Integrated Resource Plan (IRP2010) states that South Africa needs to increase its electricity generation capacity by 45 000 MW by 2030. This figure excludes Eskom’s current capa- city expansion projects.

The IRP2010 recommended that municipalities investigate energy-saving opportunities resulting from energy audits, which require a plant’s operational data and monthly electrical accounts.

Energy savings realised by implementing demand-side management programmes include a reduction in energy costs by shifting a plant’s power consumption from peak to off-peak hours. The implementation of such options at large treatment plants needs careful consideration; however, small and seasonal water and wastewater treatment plants may benefit from this strategy.

Historically, electricity efficiency measures have not been a priority in the South African water industry, owing to the rela- tively low cost of electricity.

Over the past five to ten years, this situation has been changing rapidly, owing to the country’s increased demand for energy and lack of electricity-generating infrastructure, as well as the subsequent increase in electricity costs.

The WRC notes that energy will remain a high-cost item for municipalities and utilities that operate and maintain water and wastewater processes.

“The GWRC research project is carried out by the University of Pretoria, which receives funding from the WRC,” says Van der Merwe Botha.

The commission says alternative energy sources are being considered for the maintenance of water and wastewater management in South Africa.

“Considerable work is being done on applying energy from biogas systems and from solar power technologies,” says the WRC, adding that wind power is also an option that is being investigated.

The use of mini hydroturbines in drinking water distribution networks, where high pressures are present in certain supply lines, owing to the elevated location of clean water reservoirs, is also being considered.

Energy consumption continues to increase as more people are provided with water and sanitation and new technologies are implemented to meet stricter effluent and potable water quality requirements, she concludes.

Edited by Tracy Hancock
Creamer Media Contributing Editor

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