Figure 1.
Lettuce crop coefficient for non-covered and surface covered cultivation assuming planting of seedlings after 15 days (in the graph shown as day 0).
Figure 1.
Lettuce crop coefficient for non-covered and surface covered cultivation assuming planting of seedlings after 15 days (in the graph shown as day 0).
Figure 2.
Reference evapotranspiration (ETo in mm/day) upon plain natural lighting (Köln-Bonn) or at constant radiation using (additional) artificial light.
Figure 2.
Reference evapotranspiration (ETo in mm/day) upon plain natural lighting (Köln-Bonn) or at constant radiation using (additional) artificial light.
Figure 3.
Process flow drawing of a basic DAPS layout. The blue tags comprise the RAS component, the green tags the hydroponic component, and the red tags the ANRC components. The level of each component is illustrated numerically in the small box and refers to the vertical direction the flow needs to travel to; whereas high numbers refer to high positioning and low numbers to low positioning. Gravity flow occurs, when water flows from high levels to low levels, and pressurized flow is required when the flow goes from low to high numbers.
Figure 3.
Process flow drawing of a basic DAPS layout. The blue tags comprise the RAS component, the green tags the hydroponic component, and the red tags the ANRC components. The level of each component is illustrated numerically in the small box and refers to the vertical direction the flow needs to travel to; whereas high numbers refer to high positioning and low numbers to low positioning. Gravity flow occurs, when water flows from high levels to low levels, and pressurized flow is required when the flow goes from low to high numbers.
Figure 4.
Water flow in a RAS system, whereas the tank represents the whole RAS system comprising all parts of a RAS (this is also applicable to the following figures). In terms of sustainability, the water use efficiency presents a drawback of this approach, as water is discharged to maintain an acceptable water quality for the fish. This constitutes a waste of water and nutrient resources as well as nutrient emissions. In addition, the nutrient-rich sludge often is not reused for fertilizing purposes, but instead is discharged to the sewage system.
Figure 4.
Water flow in a RAS system, whereas the tank represents the whole RAS system comprising all parts of a RAS (this is also applicable to the following figures). In terms of sustainability, the water use efficiency presents a drawback of this approach, as water is discharged to maintain an acceptable water quality for the fish. This constitutes a waste of water and nutrient resources as well as nutrient emissions. In addition, the nutrient-rich sludge often is not reused for fertilizing purposes, but instead is discharged to the sewage system.
Figure 5.
Water flow in a one-loop aquaponic system. This system approach provides the basis for aquaponics. Unlike RAS, the nutrient-rich water is not discharged, but instead used for the fertilization of a plant crop. Both components are exposed to similar water conditions. In one-loop systems the water primarily leaves the system via the crop evapotranspiration (ET
c) and the sludge. Minor water loss can be seen in the integrated water flow chart in
Figure 9.
Figure 5.
Water flow in a one-loop aquaponic system. This system approach provides the basis for aquaponics. Unlike RAS, the nutrient-rich water is not discharged, but instead used for the fertilization of a plant crop. Both components are exposed to similar water conditions. In one-loop systems the water primarily leaves the system via the crop evapotranspiration (ET
c) and the sludge. Minor water loss can be seen in the integrated water flow chart in
Figure 9.
Figure 6.
Water flow in a DAPS. As the ANRC is expected to remove most of the N, active denitrification might be needed in the RAS to reduce the nitrate concentration. This is especially the case if the water flow to the hydroponic component is not sufficient to keep the RAS water quality at a desired level. The flow chart also shows other amendments to the one-loop aquaponic system approach: (1) an ANRC that remineralizes the sludge and reduces water and fertilizer requirements; and (2) manual nutrient supplementation and nutritious ANRC nutrient outflows provide the hydroponic component with optimal nutrient concentrations that do not dilute in the whole system.
Figure 6.
Water flow in a DAPS. As the ANRC is expected to remove most of the N, active denitrification might be needed in the RAS to reduce the nitrate concentration. This is especially the case if the water flow to the hydroponic component is not sufficient to keep the RAS water quality at a desired level. The flow chart also shows other amendments to the one-loop aquaponic system approach: (1) an ANRC that remineralizes the sludge and reduces water and fertilizer requirements; and (2) manual nutrient supplementation and nutritious ANRC nutrient outflows provide the hydroponic component with optimal nutrient concentrations that do not dilute in the whole system.
Figure 7.
Fluctuation of the water composition is closely linked with the system’s nutrient input. As the main input in aquaponic systems is fish feed, aquaponic systems should be running with fish of several growth stages to ensure a close to constant uniform feed input to the system. The amount of fish does not change drastically; different fish sizes were used for illustration purposes only.
Figure 7.
Fluctuation of the water composition is closely linked with the system’s nutrient input. As the main input in aquaponic systems is fish feed, aquaponic systems should be running with fish of several growth stages to ensure a close to constant uniform feed input to the system. The amount of fish does not change drastically; different fish sizes were used for illustration purposes only.
Figure 8.
The water flow chart shows the water flows within a DAPS system. It can be seen, that the implementation of an ANRC has an impact on the water availability in the system. Even though, the water loss through evapotranspiration outweighs the loss through sludge removal, it is still an important step towards closing the cycle.
Figure 8.
The water flow chart shows the water flows within a DAPS system. It can be seen, that the implementation of an ANRC has an impact on the water availability in the system. Even though, the water loss through evapotranspiration outweighs the loss through sludge removal, it is still an important step towards closing the cycle.
Figure 9.
Flow chart for nutrients within a DAPS. The accumulation of nutrients can be allocated to edible parts of the plants, edible parts of the fish (i.e., fish fillet) and waste. The dashed line shows the impact of an ANRC on the nutrient flows. Recycled nutrients are added to the hydroponic water and can accumulate in the plant tissues, while fish are not exposed to deleterious nutrient concentrations in the water.
Figure 9.
Flow chart for nutrients within a DAPS. The accumulation of nutrients can be allocated to edible parts of the plants, edible parts of the fish (i.e., fish fillet) and waste. The dashed line shows the impact of an ANRC on the nutrient flows. Recycled nutrients are added to the hydroponic water and can accumulate in the plant tissues, while fish are not exposed to deleterious nutrient concentrations in the water.
Figure 10.
Outcome of a parameter variation experiment assessing the amount of required fish to achieve a maximum stocking density (y-axis) of 50 kg·m−3 per tank. The days are displayed on the x-axis. For this simulation, approximately 100 fish were needed to meet that objective.
Figure 10.
Outcome of a parameter variation experiment assessing the amount of required fish to achieve a maximum stocking density (y-axis) of 50 kg·m−3 per tank. The days are displayed on the x-axis. For this simulation, approximately 100 fish were needed to meet that objective.
Figure 11.
Average biomass per fish tank and total fish biomass of all fish tanks (in g; y-axis) in the RAS for the first 1000 days (x-axis). Fish biomass peaks every 50 days corresponding to the proposed harvest schedule.
Figure 11.
Average biomass per fish tank and total fish biomass of all fish tanks (in g; y-axis) in the RAS for the first 1000 days (x-axis). Fish biomass peaks every 50 days corresponding to the proposed harvest schedule.
Figure 12.
Parameter variation experiment estimating the RAS-derived N-NO3 concentration in mg/L (y-axis) based on different cultivation area (m2) options under natural light conditions. The days are displayed on the x-axis. It can be seen that 200 mg/L N-NO3 are not exceeded, when having 100 m2 cultivation area.
Figure 12.
Parameter variation experiment estimating the RAS-derived N-NO3 concentration in mg/L (y-axis) based on different cultivation area (m2) options under natural light conditions. The days are displayed on the x-axis. It can be seen that 200 mg/L N-NO3 are not exceeded, when having 100 m2 cultivation area.
Figure 13.
Parameter variation experiment for estimated N-NO3 concentration (in mg/L) when using different cultivation areas (in m2) Compared to the exclusive use of natural light, the application of artificial light for industrial production shows a different picture. The y-axis shows the RAS N-NO3 concentration, whereas the x-axis displays the days.
Figure 13.
Parameter variation experiment for estimated N-NO3 concentration (in mg/L) when using different cultivation areas (in m2) Compared to the exclusive use of natural light, the application of artificial light for industrial production shows a different picture. The y-axis shows the RAS N-NO3 concentration, whereas the x-axis displays the days.
Figure 14.
The evapotranspiration dependency for the water flow (in L; y-axis) from RAS to the hydroponic component can be seen clearly in this figure showing the flow from the RAS to the hydroponic component under natural light conditions. The days are displayed on the x-axis.
Figure 14.
The evapotranspiration dependency for the water flow (in L; y-axis) from RAS to the hydroponic component can be seen clearly in this figure showing the flow from the RAS to the hydroponic component under natural light conditions. The days are displayed on the x-axis.
Figure 15.
Dependent on the evapotranspiration rate (
Figure 14), different nitrate flows from RAS to the hydroponic component can be observed. The RAS nitrate balance in mg·L
−1 (
y-axis) for the first 1000 days (
x-axis) can be seen using exclusively natural illumination and a cultivation area of 600 m
2.
Figure 15.
Dependent on the evapotranspiration rate (
Figure 14), different nitrate flows from RAS to the hydroponic component can be observed. The RAS nitrate balance in mg·L
−1 (
y-axis) for the first 1000 days (
x-axis) can be seen using exclusively natural illumination and a cultivation area of 600 m
2.
Figure 16.
P dynamics in the hydroponic component with a cultivation area of 600 m2. The P lettuce consumption (y-axis) is assumed being constant, although this is not the case. However, this does not diminish the lettuces N total uptake. The days are displayed on the x-axis.
Figure 16.
P dynamics in the hydroponic component with a cultivation area of 600 m2. The P lettuce consumption (y-axis) is assumed being constant, although this is not the case. However, this does not diminish the lettuces N total uptake. The days are displayed on the x-axis.
Figure 17.
Accumulated P (y-axis) deficit in the system’s hydroponic component with a cultivation area of 600 m2. After 1000 days (x-axis), the deficit is almost corrected.
Figure 17.
Accumulated P (y-axis) deficit in the system’s hydroponic component with a cultivation area of 600 m2. After 1000 days (x-axis), the deficit is almost corrected.
Figure 18.
The required volume (L) of the UASB is dependent on the inflowing sludge, its SRT, and the HRT. Here, we assume that the sludge blanket covers 60% of the UASB reactor’s volume. Thus, the total filling capacity is around 140 L and serves as a good indication for sizing the reactor. The days are displayed on the x-axis.
Figure 18.
The required volume (L) of the UASB is dependent on the inflowing sludge, its SRT, and the HRT. Here, we assume that the sludge blanket covers 60% of the UASB reactor’s volume. Thus, the total filling capacity is around 140 L and serves as a good indication for sizing the reactor. The days are displayed on the x-axis.
Figure 19.
Graphical comparison between sludge production, sludge reduction, and sludge outtake assuming a TSS reduction of 90%, a HRT of 10 days, and an SRT of 80 days (y-axis). The days are displayed on the x-axis.
Figure 19.
Graphical comparison between sludge production, sludge reduction, and sludge outtake assuming a TSS reduction of 90%, a HRT of 10 days, and an SRT of 80 days (y-axis). The days are displayed on the x-axis.
Figure 20.
The hybrid decoupled system is a combination of the one-loop and the decoupled approach. Whereas the one-loop aquaponic system is regulating the nitrate of the RAS system, the decoupled hydroponic part utilizes the recycled nutrients from the ANRC. Especially for systems that focus on fish production, their advantage is that no denitrification, and thus no waste of nitrate is required.
Figure 20.
The hybrid decoupled system is a combination of the one-loop and the decoupled approach. Whereas the one-loop aquaponic system is regulating the nitrate of the RAS system, the decoupled hydroponic part utilizes the recycled nutrients from the ANRC. Especially for systems that focus on fish production, their advantage is that no denitrification, and thus no waste of nitrate is required.
Table 1.
Observed sunshine hours (per month) and the respective estimated reference evaporation (ETo in mm/day) for Köln-Bonn.
Table 1.
Observed sunshine hours (per month) and the respective estimated reference evaporation (ETo in mm/day) for Köln-Bonn.
Parameters | January | February | March | April | May | June | July | August | September | October | November | December |
---|
Sun | 73.4 | 75.8 | 187.5 | 143.9 | 168.8 | 212.1 | 209.8 | 150.7 | 135.4 | 99.6 | 68.1 | 18.0 |
ETo | 0.18 | 0.53 | 1.30 | 1.82 | 2.36 | 2.76 | 2.64 | 1.99 | 1.36 | 0.70 | 0.26 | 0.17 |
Table 2.
Optimal growth parameters for tilapia.
Table 2.
Optimal growth parameters for tilapia.
Parameter | Threshold for Optimal Growth | References |
---|
TAN (mg/L) | <2.9 | [35] |
NO2−-N (mg/L) | <0.5–1 | [36] |
NO3−-N (mg/L) | <100–200 | [37] |
T (°C) | 27–29 | [38] |
O2 (mg/L) | 4–6 | [39] |
pH | 6–9 | [38] |
Photoperiod | 18L:6D | [40] |
Table 3.
Optimal conditions for different fish in RAS (i.e., tilapia, European perch and rainbow trout), plant species in hydroponic conditions (i.e., lettuce and tomato), biofiltration efficiency being a part of RAS, and anaerobic digestion.
Table 3.
Optimal conditions for different fish in RAS (i.e., tilapia, European perch and rainbow trout), plant species in hydroponic conditions (i.e., lettuce and tomato), biofiltration efficiency being a part of RAS, and anaerobic digestion.
Sub-System | Species/Type | pH | EC (mS·cm−1) or Salinity | Optimal Temp (°C) | Ammonia (mg·L−1) | Dissolved Oxygen (ml·L−1) | Hardness (CaCO3 in mg·L−1) |
---|
RAS | Oreochromis niloticus (Nile tilapia) | 7–9 [46] | salinity: <15‰ [47] | 29.5 [32]; 27–30 [48] | <0.1 N-NH4 [48] | Optimal: 5.0 [38] | |
Oncorhynchus mykiss (Rainbow trout) | 6.5–8.5 [49] | salinity: <26‰ [50] | 15 [51,52] | <0.0125 N-NH3 [53] | ~100% [49] | >200 [54,55]; 10–400 [49] |
Clarias gariepinus (Catfish) | 7 [56] | salinity: 0‰–4‰ [57]; <4‰–6‰; optimum 0.5‰ [58] | 25–30 [58]; 28 [56] | <2.5 N-NH3 [56] | Optimal: 5–6 [59] | >20–30 [58] |
Sander lucioperca, syn. Stizostedion lucioperca (Pike-Perch) | 6.5–8.2 [60] | | 27–28 [60] | <0.40 TAN [60] | >50% [60] | |
Bio filter | Nitrobacter | 7.5 [61], 7.8 [62] | | 20–30 [63]; 24–25 [64] | | >1 [65] | |
Nitrospira | 8.3 [65] | | 29–30 [64]; 30–35 [65] | | | |
Nitrosomonas | 7.8 [62] | | 20–30 [63] | | | |
Hydroponics | Lactuca sativa (Lettuce) | 5.5–6.5 [41] | 1–2 mS/cm [41] | 21–25 [41] | <10 N-NH4 [66] | | |
Lycopersicon esculentum (Tomato) | 6.3–6.5 [67] | >2.5 reduces yield [68] | 18–24 [67] | | | |
Digester | Upflow Anaerobic Sludge Blanket reactor (UASB) | 7.4 [16,69] | | 35 [70,71] | | ~0 | |
Table 4.
Suggested hydroponic nutrient solution (ppm) vs. observed aquaponic nutrient solution (ppm) for lettuce, and the percentage difference of aquaponics with respect to optimal hydroponic conditions.
Table 4.
Suggested hydroponic nutrient solution (ppm) vs. observed aquaponic nutrient solution (ppm) for lettuce, and the percentage difference of aquaponics with respect to optimal hydroponic conditions.
System | pH | EC (mS·cm−1) | N-NO3 | N-NH4 | P-PO4 | K | Ca | Mg | S-SO4 | Fe | Source |
---|
Hydroponics | 5.5–5.8 | 1.5–2.0 | 165 | 25 | 50 | 210 | 200 | 40 | 113 | 5 | [41] |
Aquaponics | 7.0–7.6 | 0.7–0.8 | 42.2 | 2.2 | 8.2 | 44.9 | 11.9 | 6.5 | 15 | 2.5 (supplemented) | [14,72] |
Gap to Hydroponics (%) | | | 74.4 | 91.2 | 83.6 | 89 | 94 | 83.7 | 86.7 | 50.0 | |
Table 5.
Nitrogen (N) and phosphorous (P) flow from Nile tilapia feeding in RAS cage production.
Table 5.
Nitrogen (N) and phosphorous (P) flow from Nile tilapia feeding in RAS cage production.
Parameters | N (%) | P (%) | N (%) | P (%) |
---|
Neto and Ostrensky [10] | Personal Observations (RAS) |
---|
Feed | 100 | 100 | 100 | 100 |
Fish retention | 35 | 28 | 35–50 | 60–70 |
Water (Soluble Excretion) | 33 | 17 | 20–30 | 5–10 |
Total Sludge | 31 | 55 | 15–25 | 35–45 |
Thereof non-consumed feed | 18 | 18 | 5–10 | 5–10 |
Thereof feces | 13 | 37 | 10–15 | 30–35 |