Reconciling pH for Ammonia Biofiltration and Cucumber Yield in a Recirculating Aquaponic System with Perlite Biofilters

Abstract

<jats:p>Integrating hydroponic and aquaculture systems (aquaponics) requires balanced pH for plants, fish, and nitrifying bacteria. Nitrification prevents accumulation of fish waste ammonia by converting it to NO<jats:sub>3</jats:sub> <jats:sup>–</jats:sup>-N. The difference in optimum pH for hydroponic cucumber (<jats:italic>Cucumis sativa</jats:italic>) (5.5 to 6.0) and nitrification (7.5 to 9.0) requires reconciliation to improve systems integration and sustainability. The purpose of this investigation was to: 1) determine the ammonia biofiltration rate of a perlite trickling biofilter/root growth medium in an aquaponic system, 2) predict the relative contribution of nitrifiers and plants to ammonia biofiltration, and 3) establish the reconciling pH for ammonia biofiltration and cucumber yield in recirculating aquaponics. The biofiltration rate of total ammonia nitrogen (TAN) removal was 19, 31, and 80 g·m<jats:sup>−3</jats:sup>·d<jats:sup>−1</jats:sup> for aquaponic systems [cucumber, tilapia (<jats:italic>Oreochromis niloticus</jats:italic>), and nitrifying bacteria (<jats:italic>Nitrosomonas sp</jats:italic>. + <jats:italic>Nitrobacter sp</jats:italic>.)] with operating pH at 6.0, 7.0, and 8.0, respectively. With the existing aquaponic design (four plants/20 L perlite biofilter/100 L tank water), the aquaponic biofilter (with plants and nitrifiers) was three times more effective at removing TAN compared with plant uptake alone at pH 6.0. Most probable number of <jats:italic>Nitrosomonas sp</jats:italic>. bacteria cells sampled from biofilter cores indicated that the aquaculture control (pH 7.0) had a significantly higher (0.01% level) bacteria cell number compared with treatments containing plants in the biofilter (pH 6.0, 7.0, or 8.0). However, the highest TAN removal was with aquaponic production at pH 8.0. Thus, operating pH was more important than nitrifying bacteria population in determining the rate of ammonia biofiltration. Early marketable cucumber fruit yield decreased linearly from 1.5 to 0.7 kg/plant as pH increased from 6.0 to 8.0, but total marketable yield was not different. The reconciling pH for this system was pH 8.0, except during production for early-season cucumber market windows in which pH 7.0 would be recommended.</jats:p>

The use of nile tilapia (Oreochromis niloticus) cultivation wastewater for the production of romaine lettuce (Lactuca sativa L. var. longifolia) in water recirculation system

“…The high bacterial density in T3 did not affect the high removal of inorganic nitrogen (especially NH 3 ) if compared with T1 and T2. According to Tyson et al (2008), operating optimal conditions for the biofiltration process, especially reconciling pH for ammonia, was more important than nitrifying bacteria population in system.…”

“…Plants that commonly used in aquaponic are water spinach (Endut et al 2010(Endut et al , 2011Effendi et al 2015a), spinach (Shete et al 2013), Lettuce (Simeonidou et al 2012;Buzby and Lin 2014;Effendi et al 2015b;Wahyuningsih et al 2015), tomato (Roosta and Hamidpour 2011), cucumber (Tyson et al 2008;Graber and Junge 2009), and pepper (Roosta and Mohsenian 2012). Vegetable such as lettuce can be used in aquaponics system, because it can be harvested in a short time (3-4 weeks in the system), and relatively fewer problems with pests compared with fruiting plants, has low to medium nutritional requirements and is well adapted to aquaponic systems (Diver 2006, Rakocy et al 2006.…”

Comparisons between Aquaponic and Conventional Hydroponic Crop Yields: A Meta-Analysis

“…However, this might also derail the sustainability goal of AP [44]. Alternative ways of enhancing AP crop productivity without nutrient supplementation, such as anaerobic digestion of sludge that returns nutrients lost through solid waste [13], use of substrate-based systems which enhance microbial populations for improved nutrient uptake [45], and proper pH management [46][47][48], should be encouraged.…”

Nutrient Dynamics of an Aquaponic System in Southern Thailand

“…Unionized form (NH 3 ) and protonated form (NH 4 + ) are in equilibrium and the concentration of each form depends on the total concentration, pH and water temperature (Lekang, 2013;Eshchar et al, 2006;Kamal, 2006;Hargreaves & Tucker, 2004). NH 3 is prevalent at high pH and toxic to fish at levels above 0.05 mg-N/L (Tyson et al, 2008). Plants uptake NH 4 + , whereas NH 3 is a substrate for nitrification.…”