Bioponic systems with biochar: Insights into nutrient recovery, heavy metal reduction, and microbial interactions in digestate-based bioponics.

Bioponics is a nutrient-recovery technology that transforms nutrient-rich organic waste into plant biomass/bioproducts. Integrating biochar with digestate from anaerobic wastewater treatment process can improve resource recovery while mitigating heavy metal contamination. The overarching goal of this study was to investigate the application of biochar in digestate-based bioponics, focusing on its efficacy in nutrient recovery and heavy metal removal, while also exploring the microbial community dynamics. In this study, biochar was applied at 50 % w/w with 500 g dry weight of digestate during two 28-day crop cycles (uncontrolled pH and pH 5.5) using white stem pak choi (Brassica rapa var. chinensis) as a model crop. The results showed that the digestate provided sufficient phosphorus and nitrogen, supporting plant growth. Biochar amendment improved plant yield and phosphate solubilization and reduced nitrogen loss, especially at the pH 5.5. Furthermore, biochar reduced the heavy metal accumulation in plants, while concentrating these metals in the residual sludge. However, owing to potential non-carcinogenic and carcinogenic health risks, it is still not recommended to directly consume plants cultivated in digestate-based bioponic systems. Additionally, biochar amendment exhibited pronounced impact on the microbial community, promoting microbes responsible for nutrient solubilization and cycling (e.g., Tetrasphaera, Herpetosiphon, Hyphomicrobium, and Pseudorhodoplanes) and heavy metal stabilization (e.g., Leptolinea, Fonticella, Romboutsia, and Desulfurispora) in both the residual sludge and plants. Overall, the addition of biochar enhanced the microbial community and facilitated the metal stabilization and the cycling of nutrients within both residual sludge and root systems, thereby improving the overall efficiency of the bioponics.

Modified air-Fenton with MIL-88A for chemical oxygen demand treatment in used coolant oil.

Coolant oil from auto part manufacturing contains additives resulting in high chemical oxygen demand (COD) in wastewater. In this study, COD treatment of coolant oil was investigated in a metal-organic framework (MOF) with MIL-88A by a modified air-Fenton (MAF) process by varying synthetic coolant oil concentrations (1-5%), pH (3-9), air-flow rate (1-2 L/min), amount of MIL-88A (0.2-1.0 g), and reaction time (30-180 min). The results were analyzed using central composite design (CCD) and response surface methodology (RSM) using Minitab ver. 19. The characteristic MIL-88A was characterized by XRD that showed a spindle-like shape with 2θ at 10.2° and 13.0°. The FTIR spectrum revealed the vibrational frequencies at Fe-O (564 cm-1), C-O (1391 and 1600 cm-1), and C = O (1216 and 1710 cm-1). The optimum treatment efficiency was studied from 30 CCD conditions in the presence of coolant oil (5%, COD ~ 132,000 mg/L), pH (9), air flow rate (2 L/min), and MIL-88A (1 g) within 177 min. The results obtained from the experiment and the COD prediction were found to be 92.64% and 93.45%, respectively. The main mechanism of iron(III) in MIL-88A is proposed to be the production of hydroxyl radical (·OH) that oxidizes the organic matter in the coolant oil. Moreover, the MAF process was applied to the used industrial coolant oil and was found to be 62.59% efficient.

Effects of vermicompost leachate on nitrogen, phosphorus, and microbiome in a food waste bioponic system.

Food waste is rich in nutrients, such as nitrogen and phosphorus, and can be integrated with bioponics, a closed-loop agricultural system that combines hydroponics with biological nutrient recovery. Vermicompost leachate (VCL) supplementation has been shown to improve the co-composting of organic waste (i.e., compost quality) and the biodegradation of organic compounds. Thus, VCL has high potential for enhancing nutrient availability in bioponics from food waste. However, the understanding of nitrogen and phosphorus availability in food waste-based bioponics is limited, both with and without VCL. In this study, food waste derived from cafeteria vegetable waste was used as the substrate (500 g dry wt./system) in bioponics to grow lettuce (Lactuca sativa L.) for two consecutive cycles (35 days/cycle) without substrate replacement. VCL was applied weekly (1-5% v/v) and compared to the control without VCL. The results showed that the food waste in bioponics provided nitrogen and phosphorus for plant growth (15.5-65.8 g/lettuce head). Organic-degrading and nutrient-transforming bacteria (Hydrogenispora, Clostridium_sensu_stricto_1, Ruminiclostridium_1, Cellvibrio, Thauera, Hydrogenophaga, and Bacillus) were predominantly found in plant roots and residual food waste. VCL addition significantly increased nitrate, phosphate, and chemical oxygen demand levels in bioponics, owing to the nutrients in VCL and the enhancement of keystone microorganisms responsible for organic degradation and nutrient cycling (e.g., Ellin6067, Actinomyces, and Pirellula). These findings suggest that nitrogen, phosphorus, and organic carbon concentrations in an ecosystem of nutrient-transforming and organic-degrading microbes are key in managing nutrient recovery from food waste in bioponics.

Evaluation of nutrient characteristics and bacterial community in agricultural soil groups for sustainable land management.

The soil bacterial community is critical for understanding biological processes in soils and is used for agricultural soil management. The understanding of microorganisms and ecology in different soil groups classified based on soil properties (e.g., minerals, soil texture, location, nitrogen, phosphorus, organic carbon and pH, among others), is limited. To suggest soil management strategies using bacterial data, we classified soils into four groups based on physical-chemical characteristics and elucidated their relationships with soil nutrient characteristics and the bacterial community in agricultural fields in Saraburi Province, Thailand. Results show that soil groups with high bacterial diversity had positive correlations with total Kjeldahl nitrogen and available phosphorus but were negatively affected by total organic carbon and pH levels. Dominant bacterial genera included Lactobacillus, Phascolarctobacterium, Prevotella, Clostridium, Gaiellales and Blautia. Significant key biomarkers were found (p < 0.05). Nutrient-rich soil groups (high available P, acidic pH) were found with genus Agromyces, while low nutrient soil groups (low available P, basic pH) were found with Hydrogenispora, Ignavibacterium and Bauldia. Based on co-occurrence networks, organic degrading bacteria functioned with other bacteria at high degrees of interconnections, suggesting organic amendment, biostimulation and biodegradation using nutrient-rich organic substrates could be used for agricultural soil improvements.

Effects of Cu and Zn contamination on chicken manure-based bioponics: Nitrogen recovery, bioaccumulation, microbial community, and health risk assessment.

In bioponics, although chicken manure is an efficient substrate for vegetable production and nitrogen recovery, it is often contaminated with high Cu and Zn levels, which could potentially cause bioaccumulation in plants and pose health risks. The objectives of this study were to assess nitrogen recovery in lettuce- and pak choi-based bioponics with Cu (50-150 mg/kg) and Zn (200-600 mg/kg) supplementation, as well as their bioaccumulation in plants, root microbial community, and health risk assessment. The supplementation of Cu and Zn did not affect nitrogen concentrations and plant growth (p > 0.05) but reduced nitrogen use efficiency. Pak choi showed higher Cu and Zn bioconcentration factors than lettuce. Bacterial genera Ruminiclostridium and WD2101_soil_group in lettuce roots and Mesorhizobium in pak choi roots from Cu and Zn supplemented conditions were significantly higher (p < 0.05) than controls, suggesting microbial biomarkers in plant roots from Cu and Zn exposure bioponics depended on plant type. Health risk assessment herein revealed that consumption of bioponic vegetables with Cu and Zn contamination does not pose long-term health risks (hazard index <1) to children or adults, according to the US EPA. This study suggested that vegetable produced from chicken manure-based bioponics has low health risk in terms of Cu and Zn bioaccumulation and could be applied in commercial-scale system for nutrient recovery from organic waste to vegetable production; however, health risk from other heavy metals and xenobiotic compounds must be addressed.

Chicken manure-based bioponics: Effects of acetic acid supplementation on nitrogen and phosphorus recoveries and microbial communities.

Bioponics has the potential to recover nutrients from organic waste streams, such as chicken manure and digestate with high volatile fatty acid (VFA) contents through crop production. Acetic acid, a dominant VFA, was supplemented weekly (0, 500, 1000, and 1500 mg/L) in a chicken manure-based bioponic system, and its effect on the performance of bioponics (e.g., plant yield and nitrogen and phosphorus availabilities) was examined. Microbial communities were analyzed using 16S rRNA gene sequencing, and the functional gene abundances were predicted using PICRUSt. Although acetic acid negatively affected plant yield, no significant difference (p > 0.05) was noted in the average nitrogen or phosphorus concentration. In terms of nutrient recovery, the bioponic systems still functioned well, although higher concentrations of acetic acid decreased plant yield and altered the bacterial communities in plant roots and chicken manure sediments. These data suggest that an acetic acid concentration of < 500 mg/L or a longer loading interval is recommended for the effective operation of chicken manure and digestate-based bioponics.

Bioponic system for nitrogen and phosphorus recovery from chicken manure: Evaluation of manure loading and microbial communities.

Bioponics integrates the biological treatment of nutrient-rich waste streams with hydroponics. However, there are several challenges of bioponics, especially nutrient availability and qualities, which affect plant yield. In this study, chicken manure based-nutrient film technique bioponics was examined at manure loadings of 200, 300, and 400 g dry wt. per bioponic system (total of 18 plants). Bioponics effectively released nitrogen and phosphorus (total ammonia nitrogen of 5.8-8.0 mgN/L, nitrate of 7.0-11.2 mgN/L, and phosphate of 48.7-74.2 mgP/L) for efficient growth of lettuce (Lactuca sativa; total yield of 1208-2030 g wet wt. per 18 plants). Nitrogen and phosphorus use efficiencies were 35.1-41.8% and 6.8-8.0%, respectively, and were comparable to aquaponics. Next-generation sequencing was used to examine the microbial communities in digested chicken manure and plant roots in bioponics. Results showed that several microbial genera were associated with organic degradation (e.g., Nocardiopsis spp., Cellvibrio spp.), nitrification (Nitrospira spp.), phosphorus solubilization, and plant growth promotion (e.g., WD2101_soil_group, and Bacillus spp.). Nocardiopsis spp., Romboutsia spp. and Saccharomonospora spp. were found at high abundances and a high degree of co-occurrences among the microbiota, suggesting that the microbial organic decomposition to nitrogen and phosphorus release could be the key factors to achieve better nutrient recovery in bioponics.

Aquaponic Systems for Sustainable Resource Recovery: Linking Nitrogen Transformations to Microbial Communities.

Aquaponics is a technology for food production (fish and vegetables/fruits) with concomitant remediation of nitrogen-rich aquaculture effluent. There is, however, a critical need to improve the nitrogen use efficiency (NUE) in aquaponics. Here, we employed quantitative polymerase chain reactions and next-generation sequencing to evaluate the bacterial communities and their links to nitrogen transformations for improving NUEs in four bench-scale plant-based floating-raft aquaponics (pak choi, lettuce, chive, and tomato) and three pH levels (7.0, 6.0, and 5.2). Low relative abundance of nitrifiers in plant roots and biofilters suggested nitrogen loss, which decreased NUE in aquaponics. Low pH level was a major factor that shifted the microbial communities and reduced the relative abundance of nitrifiers in aquaponic systems, leading to total ammonia nitrogen accumulation in recirculating water. In plant roots, the abundance of nitrite-oxidizing bacteria (e.g., Nitrospira spp.) did not decrease at low pH levels, suggesting the benefit of growing plants in aquaponics for efficient nitrification and improving NUE. These findings on microbial communities and nitrogen transformations provided complementary strategies to improve the performance of the aquaponics regarding water quality and extent of nutrient recovery from aquaculture effluent.