Nutrient mineralization and organic matter reduction performance of RAS-based sludge in sequential UASB-EGSB reactors

Abstract

A B S T R A C TThere is a recognized need for mineralizing aquaculture-derived sludge in aquaponics systems in order to reduce waste production. Many recent studies of aquacultural waste treatment have focused only the production of biogas as opposed to the potential for mineralization of nutrient-rich sludge. Upflow anaerobic sludge blanket (UASB) reactors provide one possible solution for breaking down sludge into bioavailable nutrients that can subsequently be delivered to plants. As such, this study examines the mineralization performance of sequential UASB reactors that are designed with an expanded granular sludge bed (EGSB) and compared to standard aerobic and anaerobic batch reactors. Results of our experiments demonstrate that only chemical oxygen demand reduction is significantly different. An unexpected drop in pH of one of the three reactor systems revealed that a pH below 6 was able to significantly increase the mineralization and mobilization of nutrients. Approximately 25% of phosphorus, potassium, and calcium could also be recovered from the sludge under lower pH conditions, as compared to the mineralization performance of standard UASB reactors running at a higher pH. However, the opposite effect was observed with respect to organic sludge reduction, where diminished performance was observed in the low-pH reactor. The current study implies that anaerobic reactors operating at low pH can potentially contribute towards improved nutrient recovery in multi-loop aquaponics systems and reduction of additive agents for pH control of the hydroponic subsystem.

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.…”

“…However, there is still no consensus on how well AP crop yields compare with cHP. Whereas some studies show that aquaponically-grown crops have lower crop yields than cHP systems [10][11][12][13], other studies show that higher or similar crop yields could be obtained for aquaponics compared to cHP systems [14][15][16]. Economic assessment of AP sustainability [17][18][19] and life cycle assessment have been done elsewhere in the literature [20].…”

Fish Diets in Aquaponics

“…According to Rakocy et al (2004), fish and feed waste provide most of the nutrients required by plants if the optimum ratio between daily fish feed input and plant growing areas is sustained. Solid fish waste called 'sludge' in aquaponic systems results in losing approximately half of the available input nutrients, especially phosphorus, that theoretically could be used for plant biomass production but information is still limited (Delaide et al 2017;Goddek et al 2018). Whilst the goal of sustainability in fish nutrition in aquaculture will in the future be achieved by using tailor-made diets, fish feed in aquaponics needs to fulfil the nutritional requirements both for fish and for plants.…”

Smarthoods: Aquaponics Integrated Microgrids

“…For instance, occurring biodegradable waste streams can be treated in anaerobic reactors (e.g. UASBs) and generate both biogas and bio-fertiliser (Goddek et al 2018). Even the demineralized waste sludge can be utilised as liquid manure on conventional cropland.…”