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Recycling Water and Making Money

Wednesday, August 10, 2005

Recycling Water and Making Money

By Hassanai Kongkeo & Simon Wilkinson, ENACA

If you think that you can’t keep reusing seawater, think again: This morning we visited a shrimp hatchery that has been recycling a single batch of seawater for eleven years! Only freshwater has been added to the system to control salinity, and no water has been discharged to the environment in the history of the farm. At the same time the water quality in production facilities is amongst the best we have ever seen, and the hatchery is generating a tidy profit from its water treatment ponds by making use of the hypersaline waters to farm Artemia biomass and reclaim nutrients at the same time.

Photo: Adult Artemia harvested from the water treatment ponds.

The hatchery is owned and operated by Khun Banchong Nissagavanich, Vice-President of the Thai Shrimp Producer’s Association, and located at Banpho District, Chachoengsao Province, nearly 60 km east of Bangkok. Khun Banchong specialises in Penaeus monodon, his hatchery has never produced P. vannamei and he has no intention to start " particularly now that the price of P. vannamei has crashed. While most of the Thai industry has moved away from P. monodon and the price of postlarvae has fallen, he points out that the price of P. monodon broodstock has also fallen to about 1,000 baht (US$25) per animal from former levels of 10,000 baht (US$250).

Although it is far from the sea (30km), he selected this site for his hatchery with an aim to use recycled water to keep water quality stable, reduce the risk of viral pathogens entering the hatchery system and to avoid ongoing costs such as transportation of brine, commonly practices by many inland hatcheries in Thailand " Khun Banchong estimates that recycling water reduces his operational costs by 200,000 " 300,000 baht per month. He believes that the stable water quality is a key factor in the sustainability of a shrimp hatchery and broodstock culture. Water drawn from the sea or from estuaries may fluctuate in parameters such as pH, alkalinity, salinity, temperature and plankton content, creating stress and variation in shrimp survival rates.

Serious about recycling
Before use in the hatchery, surface water from earthen treatment ponds is pumped into 30 ton concrete tanks where it settles for a few days before salinity adjustment. On average, water salinity in treatment ponds should be around 38 ppt. In the wet season, salinity may drop to 20 ppt which requires addition of hypersaline water from the farm’s Artemia ponds to adjust it up to normal seawater salinity (30-35 ppt). In the dry season when salinity in treatment pond may rise to more than 40 ppt, it is necessary to dilute with freshwater. Then chlorine (30-50 UPN) is applied for elimination of phytoplankton and disinfection, followed by heavy aeration to eliminate residue. The treated water is pumped through an efficient filter system and ozonated before use in hatchery.

Left: Water treatment canals and ponds are aerated and lined with mangroves to assist in improving water quality. The dykes are lined with ‘pigface’, a hardy and salt-tolerant plant, to reduce erosion. Right: Seaweed is harvested from water treatment ponds on a daily basis, and composted to provide fertiliser for the Artemia ponds.

After hatchery use, water is drained to treatment ponds (0.2-0.4 ha) for sedimentation and breakdown of organic loads. Algae and seaweeds seeded in the ponds and mangroves planted around the edges assimilate some of the nutrients and dissolved organic compounds that are released. At night, aeration is also given to accelerate plant growth. Reducing nutrient loads helps prevent excessive phytoplankton blooms, which may destabilise water quality and cause shrimp mortality.

During the first two to three years of operation, water salinity in treatment ponds did not rise above 50 ppt, so not much freshwater was required for dilution to hatchery standard. However, when salinity reached 70-120 ppt in subsequent dry seasons a huge quantity of freshwater would have been required, so Khun Banchong began looking for an alternative way to use this hypersaline resource and converted two 0.5 ha treatment ponds for Artemia culture. Artemia are an ideal animal for this kind of environment, as they can grow and reproduce very rapidly in high salinity conditions where fish predators cannot survive.

Seaweed and macro algae are harvested daily from water treatment ponds and composted for a few days as a natural fertilizer. This is used to stimulate phytoplankton blooms within the Artemia ponds, upon which the animals feed. In this way the hatchery reclaims nutrients as Artemia biomass, which is sold as a secondary crop. Usually, one cycle of water treatment will take about 7-10 days.

Harvesting Artemia
The farm produces an incredible 200-600kg of Artemia biomass per day! This is sold at around 60 baht (US1.50) per kilo as feed for aquarium fish, Asian seabass nurseries and P. monodon broodstock culture. Artemia biomass is also exported, Around 80% is sold in frozen form, and 20% live.

Artemia is harvested with a very simple and effective set up: A surface-set net with bamboo guides is fixed in position behind a small, slowly rotating paddlewheel that maintains slow circulation within the pond. Artemia swimming in the surface layers are swept into the net, which is lifted and cleared periodically. The catch is transferred to small hapa-style holding cages at the pond side to await packing.

Photo: Harvesting equipment in the Artemia pond.

Looking into marine fish culture

With a practically unlimited supply of Artemia available on site Khun Banchong has recently begun experimenting with marine finfish culture; as every aquarist knows fish regard Artemia much in the same way that children regard lollies: They love it " Artemia biomass provides nutrient-rich feed (50-60% protein) and keeps water in rearing tanks relatively clean compared with non-living feed, thus contributing to higher survival. At present he is rearing mouse grouper Cromileptes altivelis in the hatchery for two months with near 100% survival (stocking densities are around 500 3cm fingerlings per 10 ton tank with excellent water quality and scrupulous hygiene) before transfer to outdoor ponds. It is early days yet, but his preliminary results are quite promising with some fish reaching 500g in 10 months of culture using live Artemia biomass as the primary feed for fingerlings held in the hatchery and Artemia mixed with trash fish in growout ponds. This is quite fast compared to a typical growout period of 18 months for C. altivelis on trash fish alone.

Above: Mouse grouper fingerlings (Cromileptes altivelis) within the hatchery. Below: Another view of the Artemia harvester, looking towards the mouth of the net.

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