Friday, 31 March 2017

UV Sterilization in Aquaponics

Aquaponics has beneficial bacteria that allow it to outperform sterile systems. Because of this, UV sterilizers are not generally used. Other negative side effects of UV sterilization include the reduction of micronutrients especially iron, boron and manganese.

"One side effect of the use of UV sterilizers is their effect on a few of the micronutrients.
Mohyuddin (1985) found that the boron and manganese contents in a nutrient solution were
reduced by more than 20% over a period of 24 h of sterilization. The most significant effect
was on iron, which was precipitated as hydrous ferric oxide. Nearly 100% of the iron was
affected." p. 100 - Hydroponic Food Production

Typical UV Disinfection System used in Aquaculture
Here is a collection of studies on the subject:

The effects of nutrient solution sterilization on the growth and yield of hydroponically grown lettuce.
Abstract: Two methods of removing bacteria from hydroponic nutrient solution [ultraviolet (UV) radiation and submicronic filter] were evaluated for efficiency and for their effects on lettuce (Lactuca sativa L.) production. Both methods were effective in removing bacteria; but, at high intensity, the ultraviolet sterilizer significantly inhibited the production of plants grown in the treated solution. Bacterial removal by lower intensity UV or a submicronic filter seemed to promote plant growth slightly, but showed no consistent, statistically significant effect.

Integrated Multi-Trophic Recirculating Aquaculture System for Nile Tilapia (Oreochlomis niloticus)
Abstract: Three densities of the sex-reversed male Nile tilapia, Oreochromis niloticus (20, 25, 50 fish/m3) were cultivated in an integrated multi-trophic recirculating aquaculture system (IMRAS) that involves the ecological relationship between several living organisms, i.e., phytoplankton, zooplankton, and aquatic plants. The results indicated that, by providing proper interdependency between various species of living organisms, the concentrations of ammonia, nitrite, nitrate, and phosphate in the system were maintained below dangerous levels for Nile tilapia throughout the cultivation period. The highest wet weight productivity of Nile tilapia of 11 ± 1 kg was achieved at a fish density of 50 fish/m3. The aquatic plants in the treatment tank could effectively uptake the unwanted nitrogen (N) and phosphorus (P) compounds with the highest removal efficiencies of 9.52% and 11.4%, respectively. The uptake rates of nitrogen and phosphorus by aquatic plants could be ranked from high to low as: Egeria densa > Ceratophyllum demersum > Vallisneria spiralis and Vallisneria americana > Hygrophila difformis. The remaining N was further degraded through nitrification process, whereas the remaining P could well precipitate in the soil sediment in the treatment tank.

Influence of UV Treatment on the Food Safety Status of a Model Aquaponic System
Abstract: Few microbial studies in aquaponics, a growing trend in food production, have been conducted to determine food safety status. The aim of this study was to determine the food safety status and the effectiveness of ultraviolet treatment (15 W, luminous flux of 900 lm) as a food safety intervention in reducing the microbial loads of the water system in a model aquaponic unit growing lettuce, basil, and barramundi (Australian Sea Bass). Sweet basil, bibb lettuce, water samples, and fish swabs were collected throughout the 118-day production period, and microbial analysis was conducted in triplicate for the presence of E. coli O157:H7, Salmonella spp., and the prevalence of aerobic plate counts (APC), coliforms, and fecal coliforms in these systems. Absence of foodborne pathogens was confirmed using ELISA technology and enumeration through petrifilms (coliform/E. coli). A significant increase was observed in aerobic plate counts over the trial period (1 to 3 log10 CFU·mL−1) in the presence and absence of UV (p > 0.05). Ultraviolet treatment did not significantly reduce the APC or coliform counts when compared to the control system samples. Future work should focus on improving the unit design, the evaluation of bio-solid filtration, and other food safety interventions.

Abstract: Aquaponics is an integrated production system where plants grow in a soil-less medium of aquaculture waste. This kind of production is seen as favourable nowadays since waste utilization could increase farm productivity and reduce environmental impacts. This research compared the microbiological quality of aquaponic water under ultraviolet (UV) sterilization and its compliance to international directives on irrigation water uses. An assessment of crop productivity was also carried out to outline differences in productive traits of lettuce (Lactuca sativa L. ‘Verde degli Ortolani’) grown in sterilized and non-sterilized aquaponic systems against a hydroponics floating system supplied with a nutrient solution of 1.6 dS cm-1. Total coliforms under UV disinfection showed counts well below 1 CFU ml-1 and a reduction in microbial loads higher than 99%. Furthermore no Escherichia coli were found in both sterilized and non-sterilized aquaponic systems. No significant differences were recorded for productive traits of lettuce (yield, mean shoot weight, shoot and root dry biomass, leaf area, specific leaf dry weight), suggesting that aquaponics is a valid method to produce vegetables with high hygienic standards.

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