Jerome Hussenot

Open-air treatment of wastewater from land-based marine fish farms in extensive and intensive systems: current technology and future perspectives

Marine land-based fish farms located in coastal wetlands (salt-pond zones, lagoon banks, etc.), whether extensive or intensive, send farm effluents directly to the sea or after short periods of stocking in retention reservoirs. The aims of our investigation have been to compare the efficiency of current and potential water treatment procedures in open-air. Wastewater retention ponds in commercial farms (Atlantic coasts of France) are efficient in removing up to 1 metric ton of particulate material (dry weight) per hectare and per day (faeces and unconsumed feed), but are inefficient in reducing dissolved wastes, both organic (urea, amino acids, protein) and inorganic (total ammonia nitrogen, phosphates). Forthcoming outdoor technology to treat these forms of waste were examined by trials at different sites: treatment by foam fractionation in extensive systems (Italian fish pond culture), treatment by microalgae production (Skeletonema costatum) and oyster filtration (Crassostrea gigas) in intensive systems (sea bass farm, Dicentrarchus labrax). It can be concluded that foam fractionation coupled with aeration and water circulation is a good way to treat and recirculate wastewaters in extensive systems, but that a multiple treatment combining a retention pond, foam fractionation and microalgae-bivalve filtration, is the best solution to treat all these forms of wastes from intensive systems.

Emerging effluent management strategies in marine fish-culture farms located in European coastal wetlands

Coastal wetlands are suitable sites for land-based fish culture in ponds and tanks, but environmental constraints on effluent discharges are stringent for these areas. In order to limit effluent loading, different techniques have been proposed and are beginning to be implemented by aquaculturists. On the Atlantic coast of Europe (France, Portugal, Spain, etc.), growout farms for sea bass (Dicentrarchus labrax), sea bream (Sparus aurata) or turbot (Scophthalmus maximus) are often located in wetlands where salt ponds were previously built. Downstream from the rearing ponds, sedimentation ponds are used to reduce particulate matter exportation. Using fish farm effluents, the continuous mass culture of microalgae has been the subject of experiments converting ammonia and phosphates into diatoms, with the systematic addition of required amounts of limiting nutrients (silicon as sodium silicate, or phosphorus as phosphoric acid). New physical treatments may be added if partial recirculation systems are employed, such as immersed foam fractionators, specifically developed for aquaculture ponds. Integrated systems may be emergent practices for reducing the effluent pollutant discharge without additional cost, in addition to producing a complementary income to that resulting from the production of the main culture species.

Water treatment of land-based fish farm effluents by outdoor culture of marine diatoms

The feasibility of using fish farm effluents was evaluated as a source of inorganic nutrients for mass production of marine diatoms. Batch cultures were conducted from May to July 1995 in 16-L outdoor rectangular tanks, homogenized by gentle aeration (0.2 Lair L−1 h−1). The effluents from the two fish farms studied were both characterized by high concentrations of inorganic materials (NH4-N, PO4-;P, Si(OH)4-Si) and were shown to support production of marine diatoms. Moreover, periodic measurements of inorganic matter levels in the cultures showed that clearance was efficacious (90% in 3–5 days). Water purification efficiency and culture productivity were further increased through appropriate nutrient balancing. When effluents were limited in silicate, addition of Na2SiO3 induced a significant increase in both diatom biomass and nutrient removal efficiency. In this case, up to 720 000 cell mL−1 were produced dominated bySkeletonema costatum. By contrast, in effluents loaded with silicate, adjustment of the N:P:Si ratio by NH4-N and PO4-P supplementation then gave increased biomass production. In this case, the maximum cell density found was 450 000 cell mL−1, dominated byChaetoceros spp.

Modeling approach of nitrogen and phosphorus exchanges at the sediment–water interface of an intensive fishpond system

Abstract The sediment–water interface in aquaculture ponds is both a sink and a source of various substances that are potentially toxic for cultured species. The sediment to water nitrogen and phosphorus exchanges were studied at the sediment–water interface in an intensive earthpond fish-farm on the French Atlantic coast. This was to define the contribution of diffusive fluxes to the total dissolved nitrogen and phosphorus produced during the 1997–1998 rearing period. Fluxes of particulate organic nitrogen (PON) and particulate phosphorus (PP) were modeled and validated using a set of observations. Diffusive fluxes were modeled using an empirical function of temperature based on in situ sediment porewater concentration profiles. An average of 15% of PON and 10% of PP, produced by fish food waste and fish faeces were sedimented in fishponds. Ammonia and phosphate diffusive fluxes (μmol m−2 h−1) were expressed as a function of temperature (T). J mod NH 4 + =(0.144T+3.49)×10 −6 exp (0.11T+16.81) J mod PO 4 3− =(0.086T+1.8)×10 −6 exp (0.09T+15.76) PON and PP stocks in the sediment decreased during the summer and increased during the winter. However, sedimentation and mineralization–diffusion processes were approximately balanced over the 2-year period. Ammonia and phosphate diffusive fluxes accounted for only 1–4% and 4–15%, respectively, of the total dissolved nitrogen and phosphorus components produced during the rearing period.