DEVELOPMENT OF A SOLAR POWERED REVERSE OSMOSIS PLANT FOR THE TREATMENT OF BOREHOLE WATER
REPORT NO 1042/1/01
The South African,Constitution dictates that every South African has the right to have access to potable water. The South Africa government has been especially active in the supply of water to township and rural areas, but the expansion of the electrical grid to supply electricity to all these areas is still lagging behind. Several alternative energy sources are being evaluated in the interim, with diesel, car batteries, LPG and paraffin power being the norm. However, these forms of energy can only be applied for low energy requirements, ie. cooking and lighting requirements or at best, the transport of potable water.
Solar power has become an effective method of supplying low cost energy to those in remote areas. It assists with the development of our country by providing electricity for household appliances, cooking utensils, heated water, etc. to those in need. Further development of solar technology, including the development of applications for solar power, is indeed a challenge for our industries.
The development of reliable solar powered DC borehole pumps has indeed helped with bringing water to people in remote areas. Several small installations, more than often in very remote areas, have made it possible to supply water from active boreholes to animals, farms and people. Unfortunately, the typical areas where the use of boreholes is required for the supply of water, are also those areas with very brackish water - not fit for human consumption.
The next logical step is therefore a water treatment unit, driven by solar power in order to render the water potable.
Reverse Osmosis, a process where an external hydraulic pressure is applied to a concentrated solution thus forcing pure water through a permeable membrane, is a novel technology used to provide purified water to industry and people. The process requires a high energy input for the high pressure feed pumps and has made it difficult to use the alternative energy sources such as those named in the first paragraph. The development and implementation of a solar powered RO unit will not only be of great benefit for communities in rural areas, but is also seen as a cost effective method of supplying potable water from brackish sources in disadvantaged and or remote areas.
The decision was made to develop a pilot demonstration unit to evaluate the feasibility of the* combined technologies; as well as the operation, application and commercialisation in the local market.
The concept is relevant to areas where small communities are spread over large areas, where the high cost of erecting large desalination plants and reticulation of desalinated water, or alternatively the piping of fresh water from other sources, is neither practically nor economically viable. The use of solar panels, which generate the power required to drive the RO unit, constitutes an initial capital investment that can be written off over the lifetime of the.unit. Results gained from the test runs with the demonstration unit will significantly contribute toward the optimisation of future units and plants of increased capacity.
The aims of the project may be summarised as follows:
Equipment and Site
The following sites were used to conduct tests for the Solar RO unit:
The reverse osmosis unit that was used for the pilot tests consisted of the following key equipment:
The following test conditions were identified to simulate or evaluate real life conditions:
The following parameters were monitored and evaluated as being relevant to the efficient operation of the unit:
The detail witn regards to each ot these parameter sets can be viewed in any ot the data sheets attached in Appendix C of the full report.
The data realised a product-per-day figure that revealed an average production of permeate under different operating conditions.
The Solar RO unit performed well under all the conditions that were evaluated. The unit proved to be easy to operate, very durable, with little maintenance required. Additional operator input did however prove to increase production even though stand-alone operation rendered excellent production figures.
The test work, mainly completed during the winter months, indicated that the unit comfortably produced at 750 l/day with little input from an operator. This is sufficient to supply a full water service to five rural units or meet the drinking water requirements for up to 50 people in a rural setting. It was shown that, in theory, this could be pushed to a maximum of 1350 l/day for a continually optimised unit. This figure would drop to a yearly average of 620 l/day for Paarl taking cognisance of historical rainfall and sunshine figures for this area. Performances for several other areas are estimated in Section 5 of the full report.
The unit proved to be well adapted to a variety of borehole water sources although it must be emphasised that high fouling waters were avoided. The dosing of pre-treatment chemicals was not required and will generally not be necessary under these operating conditions. Before the system is employed, the end user should evaluate his water source to determine his/her specific needs. The unit showed very little difference in performance at different sites considering the difference in water sources and sunlight conditions. Further tests would be required to optimise the sunlight angle required for maximum performance at a range of sites. It will be in the best interest of the end user to consult a solar power specialist to install the solar panel at an optimal angle for his/her area.
The success of the unit has made it a very viable consideration for marketing as a saleable product. The end-user will however need to evaluate the following before he/she should purchase this unit:
As a follow on for this project, it is suggested that the unit is exposed to Highveld conditions to evaluate the performance under different sunlight conditions. A range of fouling and nonfouling waters can further be evaluated along with generic or proprietary chemicals as pretreatment.