Geothermal desalination: hot rocks key to producing low cost fresh water

Geothermal energy may have the potential to produce low-cost fresh water, says a new study [1].

University of Queensland’s Geothermal Energy Centre‘s director Hal Gurgenci said geothermal-powered desalination systems could be a boon for small towns facing water shortage.

‘This is a clever combination where desalination is coupled with an agricultural function which is both cost-efficient and environmentally-friendly,’ said Gurgenci.

Gurgenci said that while some of the geothermal resources may not be hot enough for power generation, they would be a perfect fit for thermal desalination of underground brackish aquifers.

Studies indicate that for plants in the range of one to 100 megalitres (megalitre is one million litres) per day, thermal desalination technologies are more suitable than reverse osmosis especially if there is a cheap and abundant supply of heat.

Gurgenci said that technology could also be used in smaller-scale applications, and in particular in agricultural settings, a university release said.

‘Geothermal heat can be used to heat and humidify a greenhouse and produce fresh water at the same time,’ Gurgenci said.

A schematic of the process is shown below.

The brackish water is pumped and filtered from a well and sent into a ground heat exchanger where it absorbs heat from a geothermal fluid. This heat exchanger can be built of polyethylene to conserve costs.

The heated brackish water is then fed in a cascade to the first evaporator then to the second evaporator. The brine can be circulated in the circuit several times until its concentration increases over an acceptable dissolved salt concentration.

The concentrated brine is finally collected in a tank, where it is stored for later treatment or processing or reinjection.

The evaporator is the entire front wall of the greenhouse structure. It consists of a cardboard honeycomb lattice and faces the prevailing wind. Hot brackish water trickles down over this lattice, heating and humidifying the ambient cooler air passing through into the planting area and contributing to the heating of the greenhouse. Fans draw the air through the greenhouse.

Air passes through a second evaporator and is further humidified to saturation point. Air leaving the evaporator is nearly saturated and passes over the passive cooling system with a condenser (IC) immersed in a water basin.

The fresh water condensing from the humid air is piped for irrigation or other purposes. This design can be scaled up to provide 10-20 kL/day while also helping greenhouse plant growing.

[1] Mahmoudi, H. … [et al.]. (2010). Application of geothermal energy for heating and fresh water production in a brackish water greenhouse desalination unit : a case study from Algeria. Renewable and sustainable energy reviews ; vol. 14, no. 1 ; p. 512-517. doi:10.1016/j.rser.2009.07.038

Source:  IANS / Yahoo! India News, 08 Dec 2009 ; UQ News, 07 Dec 2009 ; Hal Gurgenci’s Geothermal Blog, 02 Dec 2009

Greywater reuse: water treatment kit for household grey water

A kit designed to treat household waste water for reuse could be one of the ways to tackle water scarcity in rural areas of the Middle East and North Africa, according to a Canadian organisation.

“This is a household-based technology mainly for rural areas to treat grey water that comes from the kitchen sink and bath for re-use,” said Hammou Laamrani, project coordinator at the Regional Water Demand Initiative [WaDImena] of the International Development Research Centre (IDRC), based in Canada.

[...] The kit consists of two large PVC barrels about 1.2m high, each able to contain up to 200 litres of water, pipes and sand. Before reaching the barrels, the waste water goes through a separate filter where things like small bits of food are removed. The barrels are filled with sand; there is an anaerobic digestion of the organic matter when the water goes through the sand filter and becomes cleaner.

“The quality of the treated water is improved chemically and biologically; it [the filter] removes the pathogens, particularly the E. coli that could pose a health risk. It also removes parasite eggs as they cannot go through the filter because the filter is a kind of a bio-membrane that removes all those things,” Laamrani explained.

[...] It has a socio-economic impact, it has a positive impact on the environment and it’s viable in terms of technology used,” Laamrani said.

Waste water treated by sand filter has very little nitrogen and potassium, and in terms of chemical pollution poses no risk for the soil, according to Laamrani. It is not a risk to soil because it does not have mineral components that can increase soil salinity and degradation, and it is not a risk to human beings in terms of exposure to pathogens, he said.

“It reduces the amount of water that goes into cesspits – sanitation in rural areas. So they don’t need to clean the cesspit so often – only once every three months, instead of once a week. This reduces the cost of emptying the cesspits,” he said.

“This water can also be used for productive purposes. It is used for the irrigation of saplings, particularly olive trees like we saw in Jordan… This water can also be reused in the household, like for flushing toilets,” he said.

However, it is not suitable for crops or vegetables consumed without cooking, like cucumbers and tomatoes, he said.

“The cost of the kit is $300-400, and in some cases even less depending on the price of components in any given market. If you take into account the productive use of the treated waste water and the reduced frequency of cesspit evacuation, outlay costs can be recouped in a year in places like Jordan and Lebanon,” the IDRC official said, adding that they also had projects in the occupied Palestinian territories and Yemen.

Maintenance is simple: sand in the barrels needs to be changed every 10-15 years, Laamrani said.

One of the drawbacks with the system initially was the smell: “There was no technology to remove the smell when the water was in the barrels. But it has been overcome with a new system that takes the gas out of the barrels… No longer is there a risk of attracting ants or other insects,” he said

Source: IRIN, 23 Mar 2009

See below IDRC”s Waste to Water video (in two parts) on the greywater reuse in the Middle East – Quicktime and Windowas versions are available here.

Scientists “listen” to plants to find water pollution

Scientists in Israel have discovered a new way to test for water pollution by “listening” to what the plants growing in water have to say. By shining a laser beam on the tiny pieces of algae floating in the water, the researchers said they hear sound waves that tell them the type and amount of contamination in the water. “It is a red light, telling us that something is beginning to go wrong with the quality of water,” said Zvy Dubinsky, an aquatic biologist at Israel’s Bar Ilan University. “Algae is the first thing to be affected by a change in water quality.”

[Testing algae photosynthesis] could be used to monitor water quality faster, more cheaply and more accurately than techniques now in use, Dubinsky said. [...] With proper funding, Dubinsky said a commercial product could be ready in about two years.

Related journal article: Pinchasov, Y. … [et al.] (2007). Photoacoustics : a novel tool for the determination of photosynthetic energy storage efficiency in phytoplankton. Hydrobiologia ; vol. 579, no. 1 : p. 251-256. doi:10.1007/s10750-006-0408-5

Source: Ari Rabinovitch, Reuters,14 Aug 2008

Adapting UASB technology for sewage treatment in Palestine and Jordan

High rate anaerobic technologies offer cost-effective solutions for “sewage” treatment in the temperate climate of Palestine and Jordan. However, local sewage characteristics demand amendments to the conventional UASB [upflow anaerobic sludge blanket] reactor design. A solution is found in a parallel operating digester unit that stabilises incoming solids and enriches the UASB sludge bed with methanogenic activity. The digester operational conditions were assessed by operating eight CSTRs [continuous stirred tank reactors] fed with primary sludge. The results showed a high degree of sludge stabilization in the parallel digesters at SRTs [ solids retention times] 10 and 15 days at process temperatures of 35 and 25°C, respectively. The technical feasibility of the UASB-digester combination was demonstrated by continuous flow pilot-scale experiments. A pilot UASB reactor was operated for 81 days at 6 hours HRT [hydraulic retention time] and 15°C and was fed with raw domestic sewage. This period was subsequently followed by an 83 day operation period incorporating a parallel digester unit, which was operated at 35°C. The UASB-digester combination achieved removal efficiencies of total, suspended, colloidal and dissolved CODs of respectively 66, 87, 44 and 30%. Preliminary model calculations indicated that a total reactor volume of the UASB-digester system corresponding to 8.6 hours HRT might suffice for sewage treatment in Palestine. [author abstract]

Source article: Mahmoud, N., Zeeman, G. and Lier, J.B. van (2008). Adapting UASB technology for sewage treatment in Palestine and Jordan. Water science & technology—WST ; vol. 57, no. 3 ; p 361–366. doi:10.2166/wst.2008.100