Chapter 10 Aerobic and Anaerobic Treatments for Aquaponic Sludge Reduction and Mineralisation
10.6 Conclusions
Fish sludge treatment for reduction and nutrient recovery is in an early phase of implementation. Further research and improvements are needed and will see the day with the increased concern of circular economy. Indeed, fish sludge needs to be considered more as a valuable source instead of a disposable waste.
· Aquaponics Food Production Systems10.5 Methodology to Quantify the Sludge Reduction and Mineralisation Performance
To determine the digestion of aquaponic sludge treatment in aerobic and anaerobic bioreactors, a specific methodology needs to be followed. A methodology adapted for aquaponic sludge treatment purposes is presented in this chapter. Specific equations have been developed to precisely quantify their performance (Delaide et al. 2018), and these should be used to evaluate the performance of the treatment applied in a specific aquaponic plant. In order to evaluate the treatment’s performance, a mass balance approach needs to be achieved.
· Aquaponics Food Production Systems10.4 Anaerobic Treatments
Anaerobic digestion (AD) has long been used for the stabilisation and reduction of sludge mass process, mainly because of the simplicity of operation, relatively low costs and production of biogas as potential energy source. General stoichiometric representation of anaerobic digestion can be described as follows: $CnHaOb+(n-a/4-b/2)\cdot H_2O \rarr (n/2-a/8+b/4)\cdot CO_2+(n/2+a/8-b/4)\cdot CH4$ (10.4) Equation 10.4 Biogas general mass balance (Marchaim 1992). And the theoretical methane concentration can be calculated as follows:
· Aquaponics Food Production Systems10.3 Aerobic Treatments
Aerobic treatment enhances the oxidation of the sludge by supporting its contact with oxygen. In this case, the oxidation of the organic matter is driven mainly by the respiration of heterotrophic microorganisms. COsub2/sub, the end product of respiration, is released as is shown in Eq. (10.1). $C_6H_{12}O_6 + 6\ O_2 \rarr 6\ CO_2+6\ H_2O +energy$ (10.1) This process in aerobic reactors is mainly achieved by injecting air into the sludge—water mixture with air blowers connected to diffusers and propellers.
· Aquaponics Food Production Systems10.2 Wastewater Treatment Implementation in Aquaponics
In aquaponics, the wastewater charged with solids (i.e. the sludge) is a valuable source of nutrients, and appropriate treatments need to be carried out. The treatment goals differ from conventional wastewater treatment because in aquaponics solids and water conservation is of interest. Moreover, regardless of the wastewater treatment applied, its aim should be to reduce solids and at the same time mineralise its nutrients. In other words, the aim is to obtain a solid-free effluent but rich in solubilised nutrients (i.
· Aquaponics Food Production Systems10.1 Introduction
The concept of aquaponics is associated with being a sustainable production system, as it re-utilises recirculating aquaculture system (RAS) wastewater enriched in macronutrients (i.e. nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S)) and micronutrients (i.e. iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B) and molybdenum (Mo)) to fertilise the plants (Graber and Junge 2009; Licamele 2009; Nichols and Savidov 2012; Turcios and Papenbrock 2014).
· Aquaponics Food Production Systems