Open ponds

Raceway ponds are popular algal pond systems and are the preferred production system for many of the commercial operations, including Cyanotech Corporation in Hawaii and Earthrise in California, both of which produce Arthrospira (Spirulim), as well as Seambiotic in Israel (Plate 9.1c). Excessive evaporation is a problem in these regions and a minimum depth of at least 15 cm is required to avoid a reduction in flow which can result in light limitation (Tredici, 1999). 

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In California, Spirulina sp. grown in paddle-wheel-agitated open ponds with CO2 is harvested through stainless steel screens, with recycling of the nutrient-rich water to the ponds. The wet Spirulina is spray-dried at 60°C for a few seconds to yield a food-grade product (47). 

Eliminate use of open ponds - Open ponds used to cool, settle out solids and store process water can be a significant source of VOC emissions. Wastewater from coke cooling and coke VOC removal is occasionally cooled in open ponds where VOCs easily escape to the atmosphere. In many cases, open ponds can be replaced with closed storage tanks. 

The effect may be reduced by the introduction of surfactants which tend to concentrate at the interface where they exert a stabilising influence, although they may introduce an interface resistance and substantially reduce the mass transfer rate. Thus, for instance, hexadecanol when added to open ponds of water will collect at the interface and substantially reduce the rate of evaporation. 

Cooling of water can be carried out on a small scale either by allowing it to stand in an open pond or by the spray pond technique in which it is dispersed in spray form and then collected in a large, open pond. Cooling takes place both by the transference of sensible heat and by evaporative cooling as a result of which sensible heat in the water provides the latent heal of vaporisation. 

In seasonal snow/ice storages frozen water is stored from winter to summer, when the cold is utilized. The snow/ice can be stored indoor, on ground, in open ponds/pits and under ground, Figure 200. 

If snow/ice is stored indoor it is done in a more or less insulated building. In a cavern no insulation except the ground is needed. When the snow/ice is stored on ground or in ponds it is necessary with thermal insulation, henceforth denoted insulation. Both natural and artificial snow and ice may be used and there is no size limitation for snow cooling systems. This snow cooling plant in Sundsvall is an open pond with larger pieces of wood chips as thermal insulation. 

Figure 201. Natural snow melt in open pond snow storage...

A number of different open pond snow and ice storage techniques have been suggested. In Ottawa a storage for 90,000 m3 of snow in an abandoned rock quarry (120 x 80 x 9.5 m3, L x W x H), was studied. The mean cooling load was 7,000 kW. A light colored PE plastic tarpaulin was suggested as insulation, with melt water re-circulation for cold extraction. The estimated payback time was 10 years (Morofsky, 1981). 

Biofixation of C02 by microalgae, especially as an option for the utilisation of flue gases from power plants, has been the subject of extensive investigations in the United States, Japan and Europe (IEA-GHG Biofixation Network). However, none of the related projects have demonstrated the feasibility of the concept at a pre-industrial level. What is more, C02 fixation efficiency is quite low because of the photobioreactors used in those pilot plants (raceway or open-ponds) (Figure 17). 

Once In an evaporation bed, a pesticide can adsorb to a soil colloid, undergo chemical or microbial degradation, or escape from the bed by volatilization. An evaporation bed has the potential advantage over an open pond of decreasing pesticide volatilization while allowing for Increased degradation through microbial and soil-catalyzed reactions. 

Many special types of equipment have been developed for particular industries, possibly extreme examples being the simple open ponds for solar evaporation of brines and recovery of salt, and the specialized vacuum pans of the sugar industry that operate with syrup on the tubeside of calandrias and elaborate internals to eliminate entrainment. Some modifications of basic types of crystallizers often carry the inventor s or manufacturer s name. For their identification, the book of Bamforth (1965) may be consulted. 

A Local Authority said that he would strongly oppose planning permission for construction of a WATER reservoir in this area unless the most stringent precautions were followed. Open ponds were certainly not acceptable. What would prevent people falling in them What would prevent the contents from leaking out At the very least the WATER would have to be contained in a steel pressure vessel surrounded by a leak-proof concrete wall. 

Two commercially important species of Louisiana crayfish, Procambarus clarkii and P. acutus, from the Atchafalaya River Basin, from open ponds, and from the sediment and water of these environments, were sampled three times during two consecutive fishing (production) seasons [19]. The abdominal muscle and hepatopancreatic tissue were analyzed separately. Lead, Hg, and Cd, if present, were in concentrations below the limit of detection (LoD). The heptato-pancreatic tissue contained (in p,gkg 1) Ba<8, Cu 11-15, and Fe < 640. Abdominal muscle samples had <3 p,gkg 1 of most metals. Locations with the highest levels of metal residues in sediment were not necessarily locations where crayfish had the highest levels in their tissues. 

Eliminate Coker Biowdown Pond Change operating procedures for coke drum quench and cooldown so that an open pond is no longer needed. This reduces volatile losses from the hot blowdown water. 

Salt has been of economic importance in India and is produced in laige quantities. About two-thirds of the supply comes from solar evaporation and the remainder from natural salt deposits in dry lake beds. Solar production is carried out in a series of open ponds, using hand labor and making very little effort to purify or recrystallize the salt. In addition, in some desert regions, evaporation of subsoil brine is carried out. The development of the salt industry in India was curbed by the tax on its production in fact, the first confrontation between Gandhi and the British government involved the salt tax. 

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