Studies references

Improving nutrient and water use efficiencies in multi-loop aquaponics systems

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tagstype/technical-note, region/global

12 min read

Improving nutrient and water use efficiencies in multi-loop aquaponics systems

Metadata

  • Cite key: goddekImprovingNutrientWater2020
  • Item type: Journal Article
  • Authors: S. Goddek, K.J. Keesman
  • Affiliation: Mathematical and Statistical Methods (Biometris), Wageningen University, P.O. Box 16, 6700 AA Wageningen, The Netherlands
  • Journal: Aquaculture International 28 (2020) 2481-2490
  • Date: 12/2020
  • Date added: 2021-02-04
  • DOI: 10.1007/s10499-020-00600-6
  • Funding: [not reported]
  • URL: https://doi.org/10.1007/s10499-020-00600-6
  • PDF: Goddek and Keesman - 2020 - Improving nutrient and water use efficiencies in m.pdf

Opinion

A short, conceptual follow-up to Goddek & Keesman (2018) rather than a new empirical or modelling study. It proposes one concrete engineering change (reversing the direction of the RO nutrient concentrator so it pulls from the RAS side instead of dosing the hydroponic sump, plus adding protein skimmers) and argues qualitatively for why it reduces energy use and protects nitrifying/PGPR bacteria compared with the earlier thermal-desalination design. No new mass balance, simulation, or experiment is run — the paper explicitly states the mass balance “remains the same” as the 2018 paper and that “no experimental data is available yet.” Useful as a design-rationale note explaining why the flow direction was flipped, but it contains no quantitative result of its own to cite for efficiency numbers; the SEC and RAS-discharge figures quoted are all secondary, pulled from cited sources.

Abstract

The sustainable development of agricultural systems where nutrients and water are recycled to a high degree is of enormous importance. Traditional aquaponics, where fish and plants are cultivated in one recirculating system, addresses these ecological challenges, but still struggles with its economical feasibility. Decoupled multi-loop aquaponics systems, in which the aquaculture and hydroponics subsystems are running autonomously, proved that they can keep up with the productivity of state-of-the-art hydroponics systems or even outscore them. Yet, a problem of such decoupled aquaponics systems was that plants require a high nutrient concentration, whereas fish prefer rather a clean water. In practice, the opposite is happening as the nutrients are added to the aquaculture units through the feed. This paper optimizes a recent approach showing that desalination technologies, such as reverse osmosis, can play an important role in reversing the concentrations within such systems without killing beneficial plant growth–promoting rhizobacteria thermally. The proposed integrated systems approach has the potential to make both periodical nutrient and water discharges and excessive fertilizer supplementation obsolete that would otherwise be necessary to maintain good water quality for the fish and an optimal nutrient solution for the plants.

Summary

This short paper is a conceptual refinement of the authors’ own 2018 mass-balance study on using desalination to reconcile the nutrient mismatch between fish (which need clean water) and plants (which need concentrated nutrients) in decoupled, multi-loop aquaponics. Rather than running a new simulation or a physical trial, the authors argue for two design changes to their earlier thermal-distillation concept: (1) reversing the flow direction of the nutrient concentrator so it draws from and concentrates the dilute RAS water (rather than further concentrating the already-nutrient-rich hydroponic sump), returning demineralized water to the fish side, and (2) using reverse osmosis instead of thermal distillation so that beneficial bacteria in the process water are not killed by heat, while adding protein skimmers to keep particulates out of the RO membrane and the hydroponic root zone. They state this reversal does not change the underlying mass balance already published in Goddek and Keesman (2018), only which stream is concentrated and which technology performs the separation. The paper is explicit that no experimental data exists yet for large-scale multi-loop systems, so the discussion of costs, benefits, and feasibility (electricity price dependence, avoided fertilizer and freshwater discharge, uncertain effect of RAS concentrate on plant growth) is qualitative and forward-looking rather than quantified in this paper. It closes by calling for further research into how RAS-derived concentrate specifically affects plant growth.

Review scope

  • Region / system covered: Decoupled, multi-loop aquaponics systems (RAS + hydroponics + mineralization + desalination loop); no specific geographic site, illustrated with a hypothetical tilapia RAS.
  • Argument: Reversing the RO nutrient-concentrator’s flow direction (concentrating the dilute RAS stream instead of the already-concentrated hydroponic sump) and using RO instead of thermal distillation improves nutrient/water use efficiency, protects beneficial bacteria, and can serve multiple hydroponic subsystems from one larger unit.
  • Evidence base: Builds directly on the authors’ own prior mass-balance/simulation paper (Goddek and Keesman 2018); no new primary data, no systematic literature search — supporting figures (SEC ranges, RAS discharge %) are secondary citations used as illustration.
  • Typologies or frameworks introduced: Revised process-flow schematic (Fig. 3) with a RAS-side nutrient concentrator, buffer tank, and protein skimmers, contrasted with the original hydroponic-side concentrator design (Fig. 2) from Goddek and Keesman (2018).
  • Key figures cited: MED SEC 19-27 kWh/m3 [secondary, Al-Karaghouli & Kazmerski 2012]; MSF SEC 20-37 kWh/m3 [secondary, Al-Shammiri & Safar 1999; Van der Bruggen & Vandecasteele 2002]; RO SEC 1.8-5.5 kWh/m3 [secondary, Bartman et al. 2010; Karabelas et al. 2018]; ~12% of stand-alone tilapia RAS water discharged daily to maintain water quality [secondary, Timmons & Ebeling 2013]; illustrative RO concentration example of a 4:1 ratio (5 m3 RAS water -> 4 m3 demineralized water + 1 m3 RAS concentrate) [this paper’s own hypothetical illustration, not a measured value].

Desalination technology comparison

This paper: Table 1 (p. 2484) tabulates desalination technologies by domain (electrical, thermal, mechanical, chemical, magnetic) with the most common marked in bold: electrodialysis (ED) and capacitive de-ionization (CDI) [electrical]; multiple-effect distillation (MED) and multi-stage flash distillation (MSF) [thermal]; reverse osmosis (RO) and nano-filtration (NF) [mechanical]; forward osmosis (FO) and ion-exchange resins [chemical]; energy + magnetohydrodynamics (E+MHD) [magnetic]. Text (p. 2483) states RO became competitive with thermal distillation in the 1980s and lists historical SEC ranges for MED (19-27 kWh/m3), MSF (20-37 kWh/m3), and RO (1.8-5.5 kWh/m3) — all cited from other sources, not measured here.

Compared with:

Process design: reversing the nutrient concentrator

This paper: The 2018 design (Fig. 2, reproduced here) put one desalination/distillation unit per hydroponic sump, concentrating the hydroponic nutrient solution directly and returning demineralized water to the RAS; this is described as “very energy-intensive” and requiring one unit per hydroponic subsystem. The revised design (Fig. 3) instead draws from the RAS sump (the dilute side), using a larger RO-based “Nutrient Concentrator” plus a buffer tank so a single unit can serve several hydroponic subsystems (“Sump1 … Sumpx”), with demineralized water returned to the fish tanks and concentrated nutrients (via the buffer) sent to the hydroponic sump. Protein skimmers are added before both the RO inlet and the biofertilizer/demineralized-water lines to keep particulates out of the membrane and the plant root zone. The authors state explicitly that “this inverted process flow has no effect on the system’s mass balance as described by Goddek and Keesman (2018)” — i.e., no new mass-balance calculation is performed in this paper.

Compared with:

  • #todo Delaide et al. 2019a — aerobic/anaerobic aquaponic sludge treatment, cited alongside the UASB bioreactor stages (pH 7, pH 4) shown in Figs. 2-3.
  • #todo Monsees et al. 2017a — nutrient mobilization from aquacultural sludge, cited in the same context.

Economic and sustainability discussion

This paper: Qualitative discussion only (no cost figures computed). States RO operating cost depends on local electricity price and rises with higher desired concentration (efficiency) ratios; capital costs include initial investment, maintenance, and membrane replacement; offsetting savings come from avoided periodic RAS flushing and reduced fertilizer/freshwater use. States financial savings are “strongly dependent on the location of the aquaponics system” (water availability, electricity price, discharge policy/price, produce market price, fertilizer cost) but that no location-specific analysis is performed here. Notes prior work found decoupled aquaponic leafy-green yields at least equivalent to hydroponics, but that this has not been shown for tomatoes, with a secondary indication that blossom-end rot may occur less under aquaponic conditions.

Compared with:

  • #todo Delaide et al. 2019b — pikeperch RAS wastewater effect on hydroponic tomato yield and quality, cited for the blossom-end-rot observation.
  • #todo Schmautz et al. 2016 — tomato productivity/quality across three hydroponic methods in aquaponics, cited alongside Delaide et al. 2019b for the same blossom-end-rot point.
  • Goddek and Vermeulen 2018 — cited repeatedly as evidence that decoupled aquaponic leafy-green yields matched or exceeded hydroponics; sibling paper, already/being processed elsewhere in this vault, not re-added to the chase list.

Citations to chase

  • #todo Al-Karaghouli and Kazmerski (2012) — technical/economic comparison of desalination processes; source of the MED SEC range cited here.
  • #todo Bartman et al. (2010) — RO energy-minimization control; source of the RO SEC range cited here.
  • #todo Delaide et al. (2019a) — aerobic/anaerobic aquaponic sludge treatment; context for the UASB reactor stages shown in this paper’s process diagrams.
  • #todo Monsees et al. (2017a) — nutrient mobilization from aquacultural sludge; same context.
  • #todo Delaide et al. (2019b) — pikeperch RAS wastewater effect on hydroponic tomato; source of the blossom-end-rot observation in this paper’s conclusion.
  • #todo Schmautz et al. (2016) — tomato productivity/quality in aquaponics across three hydroponic methods; cited alongside Delaide et al. 2019b.

Extraction notes

Type classification (technical-note vs. modelling vs. experiment): No fish or plant trial was run — the paper never reports collecting biological data. It also does not run a new simulation or compute any new mass balance: it states plainly that “the nutrient and water mass balance in this manuscript remains the same” as Goddek and Keesman (2018), and that “as large-scale aquaponic systems are being built, no experimental data is available yet and thus in this study, we explore different solutions to the nutrient concentration problem by following a system-thinking approach.” This rules out experiment/quasi-experiment/field-trial/exploratory (no data collected) and, in my judgment, also rules out modelling (no simulation or computation is performed in this paper — it only re-describes and conceptually reverses the flow direction of the model already published in the 2018 paper, without re-deriving or re-running it). It is not a narrative-review/meta-analysis/systematic-review either, since it is not a synthesis of others’ findings but a first-person proposal of one specific design change by the same authors as the underlying 2018 model. Weighed against the non-research options, perspective (opinion/commentary) under-describes the paper’s concrete Methodology/Process-optimization section with a redrawn system schematic (Fig. 3) and a named technical change (reversed RO flow direction + protein skimmers); technical-note (“short descriptive report, no hypothesis”) is the better fit: it is a short (10-page, mostly figures/discussion) report describing and justifying one engineering modification to a previously published design, with no hypothesis test, no new data, and no new computation of its own.

CSV outputs: Per CLAUDE.md/SCHEMA.md, only experiment, quasi-experiment, field-trial, and exploratory papers get trials.csv rows; technical-note (like modelling/review types) gets a note only. out/goddekImprovingNutrientWater2020.trials.csv and out/goddekImprovingNutrientWater2020.plant.csv are written header-only, with no data rows, because this paper reports no original measurements of any kind — every quantitative figure it cites (SEC ranges, ~12% RAS discharge, the 4:1 concentration-ratio example) is either a secondary citation or an explicitly hypothetical illustration, not a trial result.

[not reported]:

  • Funding/grant support — no Acknowledgements section and no funding statement appear anywhere in the PDF (contrast with the sibling 2018 paper, which had an Acknowledgements section naming individuals but still no funding body).
  • Any numeric mass-balance or efficiency result specific to this paper (all such values are attributed to Goddek and Keesman 2018 or to other cited sources).

[unclear]: None encountered — the paper’s own claims are stated plainly and consistently; no figures conflict with each other within this paper’s text.

Contradictions: None found rising to WARN-BLOCK/MATERIAL/CHECK severity. The paper is short, internally consistent, and does not report original quantitative results, so there is little surface for the kind of numeric contradictions this schema is built to catch. Two minor non-conflicts worth recording for completeness (not flagged, per the “target vs. measured is not a conflict” rule): (1) Zotero’s Date field for this record is 2020-12 (used as this note’s Date: field), while the PDF’s own header states “Published online: 12 September 2020” — these are ordinary online-first vs. print/issue-date values for the same article, not an internal contradiction in the paper, so not flagged. (2) The paper gives one illustrative, explicitly hypothetical RO ratio example (“A 4:1 ratio would mean that 5 m3 of RAS process water would result in 4 m3 of demineralized water and 1 m3 of RAS concentrate”) — this is presented as an example of how to read a concentration ratio, not as a measured or claimed system value, so it is not treated as a reportable data point.

Tagging judgment call: No Meta/Fish/ or Meta/Plant/ tag applied. The paper “assumes the cultivation of tilapia” only as a hypothetical illustration for Fig. 2/3’s discharge-percentage discussion (citing Timmons and Ebeling 2013 for the ~12% figure); no tilapia (or any organism) is actually studied, grown, or measured by the authors in this paper, matching the precedent set for other conceptual/design papers in this vault batch. Meta/Region/Global applied (new leaf is not needed — reused spelling seen elsewhere) because the proposed design is not tied to any specific site; the Middle East is mentioned only as context for where thermal desalination remains more common, not as the region of the proposed aquaponics application.

New tags introduced: Meta/Type/Technical-Note — new leaf under Meta/Type/; no existing note in this vault currently uses this type (existing leaves observed: Experiment, Exploratory, Field-trial, Meta-analysis, Modelling, Narrative-Review, Policy, Quasi-experiment, Systematic-Review). Title-Case leaf naming follows the existing convention. Meta/Region/Global reused as already spelled in other vault notes (e.g. tadesseComprehensiveComparisonLettuce2023, debroyModelBasedPredictive2024).

Source: Goddek and Keesman - 2020 - Improving nutrient and water use efficiencies in m.pdf

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