Rainwater and greywater systems were installed during the construction of the Liberty Complex. The practicalities involved and the savings gained are discussed.
The Liberty Complex in Umhlanga, KwaZulu- Natal, consists of Liberty Life’s regional headquarters, a Southern Sun Garden Court hotel and additional offices which will be let. The complex is saving water by collecting, storing and reusing rainwater and greywater from the hand basins, showers and baths in the hotel’s 200 rooms, and most of the office component.
JFM spoke to the piped-services consulting engineer on the project, Benatar Consulting, to find out more about the installation of these systems in general and, particularly, at the Liberty Complex and Southern Sun Garden Court Umhlanga.
Capture of rainwater optimised
The rainwater and greywater systems were designed by Lawrence Benatar of Benatar Consulting. Rainwater is collected from the roof and kept in a tank. Water from the hotel’s showers, baths and hand basins is also collected and this greywater is purified. It is mixed with the rainwater and used for the cooling towers in the air-conditioning system. The project required three separate systems of pipework – one for the rainwater, one for the greywater and another for the blackwater. However, only the rainwater and greywater is being recycled. The Geberit Syphonic rainwater system was used extensively in the design of the rainwater system. Benatar says that this system allows for the capture of more rainwater, and makes rerouting of rainwater much easier and more efficient than it would be with a conventional rainwater system. Geberit states that it uses the gravity-induced vacuum principle to create a siphonic action; allowing complete drainage of a roof area with pipes of smaller diameter than used in a conventional gravity system. According to the company, the advantages of these systems include horizontal collecting pipes, fewer stack pipes and less groundwork than conventional drainage systems. In addition, they require less space overall, reduced pipework size and fewer fittings. The roof outlets are linked together directly under the roof with a non-sloping collector pipe. Large roof areas can thus be drained through a single discharge stack. This simplifies planning and reduces construction time, Geberit notes. Cost-intensive discharge stacks and drains are not necessary so more planning options are available for the architect, the company adds.
Unconventional cleansing commended
Chem-Free Aqua supplied the ozone-purification and -treatment system which cleanses the greywater prior to its addition to the rainwater. The system differs from conventional water-treatment systems which use chemicals in that it uses ozone generators to cleanse the water.
Graham Kluk, of Chem-Free Aqua, explains the process: “The greywater is filtered before it goes into the tank where it is collected to strain it of solids. Following prefiltration, the water in the tank is circulated with ozone, which kills bacteria, and filtered through a multimedia filter.”
The multimedia filter removes contaminants such as nitrates in case someone has urinated in the shower, for instance, adds Kluk. “It ensures that the water which comes out of the system is Class 3 which is suitable for toilet flushing and irrigation purposes. The water is then pumped to the hotel for reuse.”
Ozone claims to lower cost
The advantages of using ozone instead of chemicals include lower operational costs in comparison with constant chemical use, no chemical waste and no detrimental wear on equipment and pipelines, according to Kluk. In addition, as it is manufactured for use on site, the need for storage is eliminated so the risks and hazards of storing chemicals are reduced, Kluk points out. Benatar believes that ozone sterilises and cleans water effectively, and that it is a less expensive method of achieving this. He says that it has worked perfectly so far. During the construction of the Liberty Complex in Umhlanga, rainwater and greywater systems were installed to collect, store and reuse water. Greywater is all wastewater except toilet waste and kitchen waste. All the water from the hand basins, showers and baths in the Southern Sun Garden Court Umhlanga’s 200 rooms is recycled and used for the adjacent office building’s air-conditioning system.
Levels, valves, pumps, filters and backwashing are all controlled by the PLC. There is no need to adjust anything on the system but the alarm monitors on the PLC must be checked daily.
Contamination in greywater systems is cause for concern among facilities managers. If treatment is not carried out effectively, contamination could occur, resulting in health side effects, Benatar states.“Effective disinfection is achieved by subjecting the target organisms to fixed concentrations of a disinfectant, such as chlorine, bromine or ozone, for a known period of time,” Kluk states. “Compared with conventional disinfectants, ozone achieves superior disinfection at lower chemical concentrations and within shorter contact periods.”He tells JFM that ozone is used as an oxidizing biocide to destroy microorganisms in water and to oxidise many hydrocarbon chemical compounds, as well as some inorganic contaminates such as iron and manganese. Kluk says that ozone destroys organic and toxic pollutants in water, and oxidises inorganic elements so that they can be filtered out and removed from the water supply. “The type of organisms targeted, as well as the overall ozone demand of the water, dictate the level of ozone residual required for disinfections. With the correct operating parameters and ozone dosages, an ozone system could achieve thorough disinfections at lower cost.
Why reuse greywater?
Kluk notes that all owners and operators of facilities are attempting to find ways to cut down on the use of resources such as water and, in turn, costs. Capturing and reusing rainwater and greywater – which is all wastewater except for toilet and kitchen waste – saves water.Another method is to capture and reuse blackwater – water from toilets – but this is not as popular as it is easier to treat and recycle greywater and people are more sensitive about recycling toilet waste.The Liberty complex as a whole is measuring the savings gained through meter readings but the results were not vailable at the time of writing. Benatar states that it is economical to capture greywater in a hotel because it can easily be rerouted as services are on top of each other.The payback period for a greywater system can be as early as two years, according to Benatar. “The cost of many litres of water from 200 showers, baths and basins, which are used every day, sometimes more than once, amounts to a large sum of money saved as it is not bought from the city council,” Kluk comments.There is also the added benefit that recycling greywater is a “green” solution, Kluk adds. This improves the public’s perception of the facility, and the owner and tenant foster a good reputation among those who place value on environment friendliness, Benatar says.Installing these systems is “doing what is right for the country” as there is a national shortage of water, he adds. Benatar says that the Liberty complex satisfies the requirements for a green building. He claims that, if it was audited, it would achieve close to maximum points. He says this is an important selling point should future owners or tenants want a Green Star-rated building.
Mitigating factors to consider
If the installation of a greywater system is being considered, a few factors need to be taken into account. Firstly, Benatar states that the feasibility and practicality of installing a greywater system in a facility must be investigated. Secondly, what is technically possible must be calculated in terms of what can be captured and reused.“The owners or operators of the facility must determine whether or not the manner in which the water will be reused is feasible for a particular project. Aspects such as cost and ease of maintenance, and practicalities such as space for the large storage tanks, a structure that can hold the weight of the tanks and the distance of the tanks from the point of use all need to be kept in mind.”Regarding operating costs, it needs to be understood that, although there is a saving in water costs, energy costs will increase, Benatar says. This is due to the energy required to pump the water.“A lot of people believe that they save 100 000 l and then convert that into a cost saving. However, they are not considering the additional energy cost which is incurred in order to pump that water.”
The next step is determining the use of the greywater. It can be used for irrigation, flushing of toilets and supplying an airconditioning system. “For the Liberty complex, it wasn’t feasible to do more than supply the airconditioning system because it is the biggest user of water in the entire project. None of the water can be used for irrigation or flushing toilets because it is all being used for the air-conditioning,” Benatar imparts.He says that, if greywater is used for irrigation, one has to look at hygiene as the water, which is not suitable for drinking, will be circulating in the garden and the garden taps. It is vital that the taps and pipework are identified properly as conveyors of non-potable water to avoid health risks.Using greywater for flushing toilets presents a perception problem as the water in the toilet does not look clean and is, therefore, not perceived as clean. This is why some owners and operators steer clear of this option, Benatar notes.He warns that, if the system is not designed properly and does not allow for proper evacuation of water, the building could flood, especially when the tanks are inside the building. In addition, if the filters do not function properly, an offensive odour could emanate from a greywater system, Benatar notes. Lack of maintenance will present problems, he adds.
Easy to Maintain
The rainwater system does not need maintenance and the greywater system was built to be selfbackwashing so its maintenance is minimal.
Regarding maintenance, the rainwater system does not need to be cleaned but the greywater system should be cleaned at least every five years – it should be drained and washed down with suitable cleaning products and solids should be removed, Benatar informs JFM.The greywater system was built to be self-backwashing so its maintenance is minimal, Kluk says. However, the facility’s maintenance team has to change the pre-filters once a week which, according to Kluk, should only take half an hour and does not require a specialist. “The pre-filters are reusable so a spare set is loaded into the containers and the dirty pre-filters are taken out and washed during the week so that they can be used again the following week. This keeps costs low.
Practical challenges conquered
It was a challenge to find a suitable location for the greywater tank at Southern Sun Garden Court Umhlanga, Benatar says. “It was difficult to find a position for the tank because of its size. We put it in a parking garage at the bottom righthand corner of the site. This created another challenge in routing all the greywater from the top left-hand corner to the bottom right-hand corner by gravity.”According to Benatar, a parking garage is a prime position for greywater tanks as they are normally situated below ground to enable the use of gravity, the corner spaces are usually available as it is not possible to park there and these unsightly tanks can be hidden behind concrete walls and remain completely out of sight.For drainage, fortunately, there was sufficient space to route the services to the opposite corner of the site, Benatar notes. Another challenge he mentions was not clashing with other services which were being installed, such as the air-conditioning and electrical systems. This required careful course-plotting.
Becoming more and more common
It is generally possible to retrofit a greywater system in a facility but a survey on a facility’s existing system would have to be undertaken to determine whether or not it would be possible, Benatar imparts. It also depends on the intended use of the greywater. Benatar Consulting is investigating fitting a system into a 20-year-old, 30-storey high-rise building at the moment.The size of the system could also be altered to cater for large and small facilities – even a single household. Kluk mentions that a greywater scheme was completed for a single household in Bloubergstrand where the water was used for the garden and toilets.Other installations mentioned by Kluk include the BP building on the Foreshore in Cape Town, the Woolworths and Checkers distribution centres in Midrand, the City of Cape Town’s Shared Services building in Athlone and Nedbank’s Ridgeside in Umhlanga.With many complete installations and many more to come, it seems that greywater systems are becoming popular solutions for reducing water costs.