Roof-harvested rainwater for potable purposes : application of solar collector disinfection (SOCO-DIS)

Amin, M.T. and Han, M.Y. (2009). Roof-harvested rainwater for potable purposes : application of solar collector disinfection (SOCO-DIS). Water research ; vol. 43, no. 20 ; p. 5225-5235. DOI: doi:10.1016/j.watres.2009.08.041

Abstract

The efficiency of solar disinfection (SODIS), recommended by the World Health Organization, has been determined for rainwater disinfection, and potential benefits and limitations discussed. The limitations of SODIS have now been overcome by the use of solar collector disinfection (SOCO-DIS), for potential use of rainwater as a small-scale potable water supply, especially in developing countries. Rainwater samples collected from the underground storage tanks of a rooftop rainwater harvesting (RWH) system were exposed to different conditions of sunlight radiation in 2-L polyethylene terephthalate bottles in a solar collector with rectangular base and reflective open wings. Total and fecal coliforms were used, together with Escherichia coli and heterotrophic plate counts, as basic microbial and indicator organisms of water quality for disinfection efficiency evaluation. In the SOCO-DIS system, disinfection improved by 20–30% compared with the SODIS system, and rainwater was fully disinfected even under moderate weather conditions, due to the effects of concentrated sunlight radiation and the synergistic effects of thermal and optical inactivation. The SOCO-DIS system was optimized based on the collector configuration and the reflective base: an inclined position led to an increased disinfection efficiency of 10–15%. Microbial inactivation increased by 10–20% simply by reducing the initial pH value of the rainwater to 5. High turbidities also affected the SOCO-DIS system; the disinfection efficiency decreased by 10–15%, which indicated that rainwater needed to be filtered before treatment. The problem of microbial regrowth was significantly reduced in the SOCO-DIS system compared with the SODIS system because of residual sunlight effects. Only total coliform regrowth was detected at higher turbidities. The SOCO-DIS system was ineffective only under poor weather conditions, when longer exposure times or other practical means of reducing the pH were required for the treatment of stored rainwater for potable purposes.

Article Outline

1. Introduction
2. Materials and methods

2.1. SODIS and SOCO-DIS systems
2.2. Microbial analysis

3. Results and discussions

3.1. Sampling site and characteristics
3.2. Characteristics of different weather conditions
3.3. The effects of the collector’s base angle and different backing surfaces in the SOCO-DIS system
3.4. Comparison of the SODIS and SOCO-DIS systems

3.4.1. The effects of radiation and temperature effects on microbial inactivation
3.4.2. The effects of initial pH values on disinfection efficiency
3.4.3. The effects of initial turbidity values on disinfection efficiency
3.4.4. Microbial regrowth in SOCO-DIS system and comparison with SODIS

4. Conclusions
Acknowledgements
References

Contact:

• Assistant Professor, Department of Environmental Sciences, COMSATS Institute of Information Technology, Abbottabad, 22060, Pakistan, e-mail: muhammadamin [at] ciit.net.pk
• bProfessor, Civil and Environmental Engineering Department, Seoul National University, Shinrimdong, Kwanak Gu, Seoul, 151-742, Republic of Korea, e-mail: myhan [at] snu.ac.kr

Drinking water from air humidity

Research scientists at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart working in conjunction with their colleagues from the company Logos Innovationen have found a way of converting air humidity autonomously and decentrally into drinkable water. “The process we have developed is based exclusively on renewable energy sources such as thermal solar collectors and photovoltaic cells, which makes this method completely energy-autonomous. It will therefore function in regions where there is no electrical infrastructure,” says Siegfried Egner, head of department at the IGB.

Drinking water from air humidity. Image: Fraunhofer-Gesellschaft

The principle of the process is as follows: hygroscopic brine – saline solution which absorbs moisture – runs down a tower-shaped unit and absorbs water from the air. It is then sucked into a tank a few meters off the ground in which a vacuum prevails. Energy from solar collectors heats up the brine, which is diluted by the water it has absorbed.

Because of the vacuum, the boiling point of the liquid is lower than it would be under normal atmospheric pressure. This effect is known from the mountains: as the atmospheric pressure there is lower than in the valley, water boils at temperatures distinctly below 100 degrees Celsius.

The evaporated, non-saline water is condensed and runs down through a completely filled tube in a controlled manner. The gravity of this water column continuously produces the vacuum and so a vacuum pump is not needed. The reconcentrated brine runs down the tower surface again to absorb moisture from the air.

“The concept is suitable for various sizes of installation. Single-person units and plants supplying water to entire hotels are conceivable,” says Egner. Prototypes have been built for both system components – air moisture absorption and vacuum evaporation – and the research scientists have already tested their interplay on a laboratory scale. In a further step the researchers intend to develop a demonstration facility.

Source: Fraunhofer, June 2009

For an overview of Atmospheric Water Generators (AWG) see the Wikipedia entry on this technology.

Most AWGs seem to be commercial systems sold in developed countries, although WaterMaker (India) Pvt. has installed an AWG system in the Indian village of Jalimudi.

A different technology to collect water from the air is fog collection, which has been widely used in developing countries in coastal areas in Latin America (Chile, Ecuador, Peru) and Southern Africa, and in mountainous areas such as Nepal. See the entry and links in the Akvopedia item on fog collection.

WaterAid water source options poster

WaterAid has produced a new poster resource that rates different water supply technology options in relation to their relative capital cost, operational cost, water quantity supplied and water quality supplied.

The poster also provides information on the situations in which certain water supply technologies are most applicable.

Levels of appropriateness are colour coded based on different combinations of the above variables.

The resource can be printed as a poster on A4, A3 or A2. You can download it here:

Water source options – a comparison ( PDF 93KB)

Fog harvesting: a solution for Cape Verde’s water shortages?

When the rainy season ends in Cape Verde hundreds of families tap into another source of water: fog harvesting. Farmers track fog as their ancestors followed rain clouds, monitoring 15 double-sided nets that rise into the mountains.

[...] [R]esidents here have little access to safe drinking water due to a shortage of purification facilities and declining rainfall, a situation shared by 25 percent of the population – more than 100,000 people.

Close to the sea, the government-protected park on Santiago Island has ample fog, which does not often produce rain.

With the help of 200sqm of netting erected in 2005, Serra Malagueta’s residents are collecting fog water to supply their water needs. The nets capture fog, which then turns into water that drips into a trough and flows through pipes. The filtered water is fed into holding tanks that supply the water to the elementary school and community faucets.

Before fog nets families waited during the dry season for water to be trucked in from surrounding communities that have clean groundwater, for which they paid 2 US cents per litre. Most of the country’s water must be purified at energy-intensive production plants. It costs about $1 to desalinise 1,000 litres of water, according to the government. The state electricity company spent nearly $4 million dollars on water purification in 2006.

[...] Antonio Sabino, a local water engineer who tested fog nets 20 years ago for the National Institute of Agricultural Development and Investigation, told IRIN the nets offer a cheaper solution to cover the island’s water needs. “There is no pollution, no need for [purification-desalination] pumps, fossil fuels or motors.”

He estimated that on a windy, foggy day the 15 nets can produce more than 4,000 litres of water at a fraction of the cost residents paid for trucked-in water. Sabino told IRIN each net costs about $800, which includes labou rand a filter and net screen made from locally-available materials.

Portuguese engineers first experimented with fog nets in Cape Verde during the 1960s. A decade later, Dutch companies tried to revive fog water “harvesting,” but the trend again faded.

Water engineer Sabino said the risk scares people away. “All hydrology requires risks. Building fog nets require overhead investment and they may not provide as much water as expected.” But he said it is a bigger risk to not invest in alternative water sources. “Using subsoil resources without letting them recharge is like taking money out of a bank without ever depositing more money.

“Cape Verde has some zones that offer optimal [fog] conditions – some of the best in the world. The areas are small, but these small areas have enormous potential.” The engineer said Cape Verde’s more than 1,000 hectares of land is sufficiently foggy to produce billions of litres of affordable clean water per year.

Currently Serra Malagueta is the only community doing fog-harvesting.

Starting in November, Saharan desert winds from northern Africa blow dust onto the nets, making it harder to ensure water quality. Sabino said it is important during this period to change the filters, clean the nets and check water quality.

Also, there is not year-round fog in Cape Verde, which markets itself as a sunny tourist destination. “Nets should be built with sufficiently large dimensions to produce enough water to accommodate these periods,” advised Sabino.

For more info on fog harvesting see the FogQuest web site. In 2010 the 5th International Conference on Fog, Fog Collection and Dew will be held in Münster, Germany.

Source: IRIN,: 09 Jan 2009

Sand dam technology: A key to dousing seasonal water conflicts?

The new Akiriamet [West Pokot Region, Kenya] sand dam, [completed on 04 April 2008 in ] is one of several either completed or being constructed in the more arid, water-challenged regions of Kenya and across the border in neighboring northern Uganda, as part of the African Water for Life/Water for Peace program of the global humanitarian agency Church World Service (CWS).

The sub-surface dams are a simple but highly effective technology that involves constructing a concrete dam under the surface of a dry riverbed. A sand dam, which costs about US$5,000 to construct, slows the flow of water in the riverbed during the rainy season, causing more water to sink into the sand, which produces an underground reservoir of clean water.

Sand dams can hold up to 2.6 million gallons of water and provide clean water for a thousand or more people, for livestock and for gardens.

Source: Reuters, 07 Apr 2008

Meteorology: Taming the sky

Is it really possible to stop rain, invoke lightning from the heavens or otherwise manipulate the weather? Jane Qiu and Daniel Cressey report on the once-scorned notion of weather modification.

[...]

China has one of the largest programmes for weather modification in the world. It spends between 400 million yuan (US$60 million) and 700 million yuan a year on it, and employs 32,000 people to operate 35 specially equipped planes, 7,000 anti-aircraft cannons and 5,000 rocket launchers. Official figures from the China Meteorological Administration say that the country created 250 billion tonnes of rain between 1999 and 2006, an annual production of more than 30 billion tonnes. This is enough to meet the needs of more than 500 million of its 1.3 billion people, but the country aims to generate 50 billion tonnes a year by 2010.

Many researchers, both in and outside China, doubt that sufficient evidence has been accumulated to support this claimed success. “In fact, China is very much behind in this area,” says Zhang Hong-fa, an atmospheric scientist at the Cold and Arid Regions Environmental and Engineering Research Institute in Lanzhou. “A false sense of achievement would impede genuine progress.”

Read more: Nature, 453, 970-974 (2008) – doi:10.1038/453970a – Published online 18 June 2008

Beetle-Based Water Harvesting

A pioneering water harvesting system inspired by the Namib Desert Beetle is one the biomimicry innovations that will feature in the first annual edition of Nature’s 100 Best© book. The book is an initiative of ZERI, Biomimicry Guild and the Biomimmicry Institute, in cooperation with IUCN, and UNEP.

The Namib Desert beetle lives in a location that receives a mere half an inch of rain a year yet can harvest water from fogs that blow in gales across the land several mornings each month. A team from the University of Oxford and the UK defense research firm QinetiQ, have designed a surface that mimics the water-attracting bumps and water-shedding valleys on the beetle’s wing scales that allows the insect to collect and funnel droplets thinner than a human hair.

The patchwork surface hinges on small, poppy-seed sized glass spheres in a layer of warm wax that tests show work like the beetle’s wing scales.

Trials have now been carried out to use the beetle film to capture water vapour from cooling towers. Initial tests have shown that the invention can return 10 per cent of lost water and lead to cuts in energy bills for nearby buildings by reducing a city’s heat sink effect.

An estimated 50,000 new water-cooling towers are erected annually and each large system evaporates and loses over 500 million litres.

Other researchers, some with funding from the US Defense Advanced Research Agency, are mimicking the beetle water collection system to develop tents that collect their own water up to surfaces that will ‘mix’ reagents for ‘lab-on-a-chip’ applications.

Source: UNEP, 28 May 2008

Rooftop Rainwater Harvesting Systems

For over 20 years, the Barefoot College, India, has helped rural communities to develop their own rainwater harvesting systems and community-managed water supplies:

· In India, nearly 1300 systems in 17 states with a total storage capacity of 47 million liters provide clean water to over 235,000 school children in remote, rural communities.

· In Afghanistan and 5 countries in Africa, 15 rainwater systems constructed since 2006 with a total storage capacity of 1.5 million liters provide clean water to over 4,200 school children.

In their February 2008 newsletter, the Barefoot College gives an overview of their current rainwater harvesting projects, with links to pictures on the construction of a 100.000 litres rainwater tank in Sierra Leone and General Guidelines for Construction of a Rainwater Harvesting Tank in Schools.