Tuesday, November 07, 2006 Speak out: Desalination By Engr. Soekarno Tecson University of San Carlos
THE scarcity of potable water continues to be a serious concern. With the increasing urbanization of Metro Cebu, groundwater sources are being depleted.
The recent move of the Metropolitan Cebu Water District (MCWD) to develop nine more exploratory wells to augment supply, with or without the Carmen Bulk Water Supply Project, cannot be considered a strategic investment.
While the need to meet the current water demand is apparent, increasing groundwater extraction is not an environmentally compatible solution.
There is alternative water source, and this can be found through desalination of brackish water or seawater by reverse osmosis (RO). But this has always been regarded as a costly option.
At first glance, seawater desalination is one of the costliest process when compared with other sources. However, the comparison is deceiving because many costs are not accurately computed into the estimates for groundwater source production. Environmental impacts are not factored in, along with the need for rotational capacity to back up these groundwater supply systems during drought and emergencies, such as contamination of the source.
There are also major regulatory and political hurdles to be overcome when implementing groundwater supply projects.
Transporting water from adjacent towns is also very contentious and promotes ill will between neighbors.
The rationale for suggesting desalination is obvious when one observes high growth rate in coastal communities of Metro Cebu. The significant advantage of desalination is the proximity of the point of use from the point of withdrawal. This will have an edge in systems recovery rate value against the 60 percent or less that MCWD usually achieves with present supply sources situated farther inland. In addition, seawater source has limitless potential for supply without causing permanent environmental damage in the host area and the possibility of a water war.
Reverse osmosis technology has already matured and is now used extensively in other countries, especially those that have their share of environmental overloads. Getting additional 1,000 cubic meters per day of potable water through seawater desalination RO system, instead of from nine more water wells, is believed to have long term benefits.
RO system design is modular and subsequent increases in capacity can be done in less than a year. Also, the bulk components of an RO system can easily be fabricated locally. As for energy use, which make up 55 to 60 percent of operating costs, there are innovative power recovery schemes that can reduce cost by 30 to 40 percent through the recovery and re-utilization of residual pressure of the reject stream prior to discharge.
Estimated production cost for desalinated seawater is about P45 to P50 per cubic meter. It is expected that MCWD will give the realistic “blended water costs” to the consuming public. The blended water costs will be P43.60. The P1.60 per cubic meter increase in consumers’ water bill would not be noticed if the standard of sufficiency in potable water supply is attained.
All things considered, seawater desalination by RO process is a technically and economically viable alternative to supply the needs of Metro Cebu and must be considered as a serious option.
