Liquid Anaerobic Digestate as Sole Nutrient Source in Soilless Horticulture-Or Spiked With Mineral Nutrients for Improved Plant Growth

Substituting phosphorus and nitrogen in hydroponic fertilizers with a waste derived nutrients solution: pH control strategies to increase substitution ratios

Hydroponics, despite its potential for efficient crop production, relies heavily on chemical fertilizers derived from nonrenewable resources and thus contributes to environmental burdens and unsustainable use of phosphorus. Integrating hydroponics into a circular phosphorus economy is crucial for mitigating these impacts. This study quantitatively assessed the capacity of filtrates from nitrified biogas digestate (f-NBD), a nutrient solution derived from organic waste, to replace phosphorus and nitrogen in hydroponic chemical nutrient solutions. Additionally, the influence of pH control methods on phosphorus recovery and substitution was investigated using a novel pH-rebound approach involving acidification followed by alkalinization to pH 6. The experimental results demonstrated that the pH-rebound method effectively dissolved apatite phosphorus, the predominant form of precipitated phosphorus in NBD, without inducing significant reprecipitation upon alkalinization. This pH adjustment enhanced the phosphorus solubility and optimized the nitrogen-to-phosphorus (N/P) ratio in f-NBD, enabling it to substitute up to 77% of the phosphorus and 100% of the nitrogen in standard hydroponic nutrient solutions. The study also revealed that, under certain conditions, f-NBD is as a more viable option for phosphorus recovery than struvite, a widely recognized recovered phosphorus product. The identified substitution ratios and pH optimization strategies provide valuable insights for mitigating the environmental burdens of hydroponic fertilizers. By partially replacing chemical nutrient solutions with f-NBD, hydroponics can be integrated more effectively into a circular phosphorus economy, reducing the reliance on nonrenewable resources and curtailing the environmental impacts associated with the production and use of conventional fertilizers. This research provides a basis for future initiatives aimed at developing sustainable hydroponic systems and offering new utilization methods for biogas digestate.

Nutrient recovery from wastewater for hydroponic systems: A comparative analysis of fertilizer demand, recovery products, and supply potential of WWTPs

Nutrient recovery from wastewater treatment plants (WWTPs) for hydroponic cultivation holds promise for closing the nutrient loop and meeting rising food demands. However, most studies focus on solid products for soil-based agriculture, thus raising questions about their suitability for hydroponics. In this study, we address these questions by performing the first in-depth assessment of the extent to which state-of-the-art nutrient recovery processes can generate useful products for hydroponic application. Our results indicate that less than 11.5% of the required nutrients for crops grown hydroponically can currently be recovered. Potassium nitrate (KNO3), calcium nitrate (Ca(NO3)2), and magnesium sulfate (MgSO4), constituting over 75% of the total nutrient demand for hydroponics, cannot be recovered in appropriate form due to their high solubility, hindering their separated recovery from wastewater. To overcome this challenge, we outline a novel nutrient recovery approach that emphasizes the generation of multi-nutrient concentrates specifically designed to meet the requirements of hydroponic cultivation. Based on a theoretical assessment of nutrient and contaminant flows in a typical municipal WWTP, utilizing a steady-state model, we estimated that this novel approach could potentially supply up to 56% of the nutrient requirements of hydroponic systems. Finally, we outline fundamental design requirements for nutrient recovery systems based on this new approach. Achieving these nutrient recovery potentials could be technically feasible through a combination of activated sludge processes for nitrification, membrane-based desalination processes, and selective removal of interfering NaCl. However, given the limited investigation into such treatment trains, further research is essential to explore viable system designs for effective nutrient recovery for hydroponics.

Effect of solar and artificial lighting on microalgae cultivation and treatment of liquid digestate

A comparative study was carried out to assess the effect of two light sources on microalgae cultivation and the treatment of liquid digestate. The R1 photobioreactor operated with LED lightning allowed to achieve moderate nutrient removal rates whereas soluble COD (Chemical Oxygen Demand) was reduced in 90%. After switching this reactor into sunlight, the removal rate of phosphates increased to 66%. However, the greatest removal rate of both nutrients and sCOD of up to 93% was observed in the R2 photobioreactor operated only under sunlight. Microglena sp. was the dominant algae growing in the R1 reactor, and the main bacteria families detected were Chitinophagaceae, Sphingomonadaceae and Xanthobacteraceae. In contrast, Tetradesmus obliquus dominated in the R2 reactor and Rhodanobacteraceae, Chitinophagaceae and A4b were predominant bacteria in this run. Furthermore, much greater biomass productivity as well as overall biomass density was observed in the R2 photobioreactor cultivated exclusively with solar lightning.

Biochar-enhanced agricultural application of liquid digestate from food waste anaerobic digestion for celery cultivation

In this research, the performance of biochar-enhanced agricultural application of food waste liquid digestate for celery cultivation was investigated to reveal its utilization potential and environmental impacts. Liquid digestate demonstrated a good agronomic effect, with a significant fertilization efficiency of 42.3 % during celery growth. With liquid digestate addition (270 t/ha), the same level of harvested celery yield of 15,345 kg/ha was achieved compared with chemical fertilizer utilization of 15,495 kg/ha. Based on the same nitrogen input, the liquid digestate application increased the sugar content of the harvested celery (7 %-15 %) while decreasing the nitrate content (29 %-45 %). The harvested celery with liquid digestate application indicated higher contents of total nitrogen, total phosphorus and total potassium levels than those in the chemical fertilizer group. Liquid digestate as a fertilizer supplemented the soil with nutrients, including phosphorus, potassium and organic matter, but did not cause excessive accumulation. The inorganic nitrogen content of the leachate increased as applied liquid digestate increased. However, it remained 20 %-60 % lower than that of chemical fertilizer at the same fertilization efficiency. After applying liquid digestate, there was no significant increase was observed in soil salinity. The coupled addition of biochar helps to improve the overall effects of liquid digestate for agricultural application and reduce negative environmental impacts. This study demonstrates that returning liquid digestate to agricultural fields as fertilizer is an environmentally and economically beneficial practice.

An integrated leachate bed reactor - anaerobic membrane bioreactor system (LBR-AnMBR) for food waste stabilization and biogas recovery

This study developed an integrated LBR - AnMBR system for efficient stabilization and biogas recovery from food waste (FW) at room temperatures (21-22 °C). First, the leachate recirculation rate (4.4-13.2 L/h) was optimized to maximize hydrolysis and acidification yields. The maximum hydrolysis yield of 551 gSCOD/kg VSadded was achieved at recirculation rate of 13.2 L/h. The VFA concentrations in the FW leachate was as high as 12.5-16.0 g/L, resulting in a high acidification of 468 g CODVFA/kg VS. The solubilized FW was further stabilized by feeding the leachate to AnMBR. Different hydraulic (HRT) and solids retention times (SRT) were tested to achieve high COD removal and methane yields. High COD removal of 86 ± 3% was obtained in the AnMBR at HRT of 13 and SRT of 75 days. High biogas recovery of about 850 kWh per ton FWtreated was achieved along with high quality of AnMBR permeates containing low COD concentration but advantageously high concentration of nutrients (NH4+-N 317-403 mg/L, total phosphate 23-213 mg/L) without any particulates, which can be reused for landscape or liquid fertilizer.