Commercial Rainwater harvesting
Rainwater harvesting has been practiced for thousands of years. The purpose has always been water security for humans and their crops. Slowly it migrated to decentralized systems where a small community or property will harvest rainwater for drinking and cooking purposes. The advent of municipal water systems removed the need for rainwater harvesting as water was collected from an area hundreds of kilometers away from point of use and supplied in purified form to the user.
Factors such as drought, old water infrastructure, population growth and concerns for municipal water supplies as well a trend in in green buildings, have contributed to a demand for commercial rainwater harvesting systems. Many projects have been put in place that would capture rainwater, grey-water, and other on-site water sources for reuse. Captured water is purified sanitized and pressurized for safe reuse. Big industrial factories simply harvest water and use it in their production process as it does not require to be of potable water standard. A well designed commercial system can save thousands of kiloliters in municipal water every year for the life of the building.
Early adopters of rainwater harvesting systems have been small factories, schools and many government building. Unfortunately many projects have been implemented purely to satisfy a green building code rather than to critically look at ways to maximize rainwater harvesting and reducing water consumption.
Some of the first projects are always rainwater harvesting systems that will use the water for non potable use. This requires a dual plumbing system in buildings and can be costly to retrofit. It is therefore beneficial to incorporate it into the design of a new building. Companies are also gradually moving away from water intensive gardens and are planting indigenous plants that require less irrigation. Many old rainwater harvesting systems purely focused on replacing municipal water with harvested rainwater to be used in the irrigation systems when water was available.
The recent drought in Southern Africa has put the water security agenda back on the table. With municipalities losing between 25% and 40% of their water through ageing infrastructure and poor maintenance many companies are concerned about water security. Any interruption in water supply can have a major impact on productivity and production capability.
The biggest challenge and cost in any commercial rainwater harvesting systems is space and cost for storage. Generally above ground space is at a premium thus all the rainwater tanks need to be installed underground. To effectively harvest rainwater the sizing of the storage tanks are critical. It is always better to have more than less storage space as you want to maximize the rainwater recovery when it rains. Thus the tanks, the building and installation cost thereof can be as much as 50% - 60% of the total project cost.
In Southern Africa it is good practice to also use the rainwater tank as a backup water storage tanks and design the system in such a way that the tanks always maintain a certain level of water (municipal or rainwater). Should a water interruption take place the property will thus always have a backup water source for a period of time.
Water application and treatment is often overlooked. In a well designed system the quality of rainwater is so good that it can easily be converted into potable water without the use of chemicals. Converting harvested rainwater into potable water circumvents the need for a dual plumbing system and purified rainwater will simply replace municipal water when it is available and vice versa.
The need and implementation for commercial rainwater harvesting systems are growing. It is thus very important that companies with experience in the design and instillation of these system are involved at an early stage of a new project. Our experience has shown that these projects have a payback of less than ten years at current water prices. As water becomes more scarce, expensive and supply not reliable the benefits far outweigh the cost.
Factory harvest 10 million liters of rainwater
BSN Medical in South Africa a multinational company embarked on a global green initiative with the objective of reducing their impact on the environment as well as reducing their operational costs. The Tizagenix water division was selected to design and install a mega rainwater harvesting system at their Pinetown factory in Durban South Africa.The installed system has recovered over 10 million liters of rainwater during the past 12 months.
The objective of the project was to design and install a rainwater harvesting system to recover rainwater from hard-surface areas totaling 16000m2. The recovered water is used as process water in the factory.
Rainwater recovered from the factory roof drain into a 500mm storm-water pipe system 3.5m below ground where it had to be recovered filtered and transferred to an above ground rainwater storage tank. From the storage tank the water had to be treated and used as process water for boilers, cooling towers and other non potable process water applications.
Rainwater harvesting for warehouses, factories and Industrial parks
Factories, warehouses and big industrial and or commercial surface areas provides the ideal opportunity for rainwater harvesting. Unfortunately, new warehouses and industrial parks are still being built today without any form of rainwater recovery and the rainwater is merely discharged into the storm-water attenuation system for discharge into the natural water systems.
Integrating a system for large scale rainwater harvesting into the design of a warehouse is very cost effective and can significantly reduce the water consumption of the property. Many of these facilities have sufficient surface area on site to recover rainwater for the total water requirement for the premises.
Installing a rainwater system and integrating it into the design will reduce their operational risk of water interruptions and can realize significant financial benefits that a water saving initiatives can provide.
In many instances rainwater harvesting from the roof surface of the warehouses and using the rainwater that fall on the premises will offset the operational water consumption of the site.
Rainfall patterns vary and therefore rainwater has to be recovered and stored to recover water as best as possible for periods when there is no rain.
Prior to the design of a system for an industrial complex the current or future use water application use of the facility need to be well understood. It will determine how the rainwater is recovered and how it is used for maximum benefit.
Single warehouse rainwater harvesting recovery
This is most probably the simplest for of recovery. The warehouse must have a gutter system or some of water transport system installed that can redirect rainwater to single or multiple collection points. The benefit of this as that all water is recovered from the roof surface where there is minimum contamination. Once all the harvested rainwater is correctly redirected it can be dynamically filtered and immediately transferred to a suitable rainwater storage tank or facility for further processing and use.
All new warehouse facilities require some form of stormwater attenuation before discharge into the stormwater system, thus the systems must also be designed to cope with flooding conditions automatically.
Multiple buildings, warehouse and factory rainwater harvesting recovery.
The harvesting of rainwater off multiple building is more complex. In many instances the rainwater from all surfaces (roof, roads, gardens etc.) is discharged into storm-water system with some form of attenuation before it flows into a central municipal storm-water system toward a natural stream or river. This water is generally contaminated with rubbish, and other surface spills like oil, diesel etc. that is washed off the road surface. It will also contain soil and silt.
The primary focus of a system that will dynamically harvest the storm-water will be to remove or filter out as much of the rubbish and other solid contaminants before the water is recovered. There are various technologies available to do it, however these systems must be self-cleaning and be able cope with flood conditions.
The recovered water can then be stored and treated for use. The most cost-effective way to treat this water is to filter it with a combination of sand and bag filtration and then re-use the water in industrial heating and cooling applications. Generally, rainwater is very soft and requires minimum treatment before use e.g., in a boiler. It is possible to further treat the water to potable standard but it requires energy and multiple storage tanks. The benefit of treating it to potable standard is that it can simply be piped into the existing factory warehouse supply (ensuring that it complies for legislation and necessary permit applications)
Example of Wisy commercial rainwater system
BISHOPS BUILDING
The Bishop Building on the Saint Francis South campus, honoured by AGC of Oklahoma with a 2010 Build Oklahoma Award, has been cited as the first registered LEED (Leadership in Energy and Environmental Design) Gold Certified project in Oklahoma. The LEED Gold Certification was awarded by the U.S. Green Building Council in September. Gold is the second highest level. It is the first gold-certified health-care facility in Tulsa; there are only two in the state and a handful in the United States. The Bishop Building is a five-story, 110,000-square-foot medical office building and a multilevel parking structure. The building includes an enclosed bridge connector between the hospital and the building. Rainwater is filtered, stored and then used for irrigation of the native landscape plants.
Personal Care factory use purified rainwater in products
Our company installed and commissioned a rainwater harvesting system at a Personal Care factory in Durban where the purified rainwater is used exclusively for manufacturing of Personal Care Products.
The rainwater water is recovered off a 5200sqm roof filtered via two WISYWF150 25 micron primary filters before transfer to four 10 000l rainwater storage tanks. From the storage tanks the water if filtered and purified using a 4 step water purification process before it is transferred to a 5000l intermediate water storage tank.
Read more: Personal Care factory use purified rainwater in products
