Biochar is a promising pyrolysed carbon-enriched soil amendment and has excellent properties for agriculture production and to remediate environmental pollution. A set of reviews were conducted on biochar production by pyrolysis process from various waste biomass which has drawn extensive interest due to the low cost of production with several benefits. As many potential technologies have been developed, there are still several knowledge gaps that have been identified for some key points to contribute a comprehensive study towards soil fertility, nutrient and water retention, soil microbial activity, plant growth and yield, pollution remediation, mitigation of greenhouse gas emission and an improvement in the farmer’s economy to achieve maximum profit by adopting environmentally friendly technique “pyrolysis”. Therefore, this review explored a detailed study on food waste biochar production by the pyrolysis process and its impact on different applications as an amendment. Slow pyrolysis process at low and medium temperatures is a potential amendment for agriculture production and soil and water remediation by enhancing biochar properties like carbon, BET surface area, cation exchange capacity, zeta potential, and nutrient content, etc. with minimum ash content. The biochar enhances soil water and nutrient retention capacity, crop yield, and improved microbial community at different soil quality. Additionally, food waste to biochar is a realistic adsorbent and economical carbon sequester to mitigate GHG emissions. This review conducted a brief assessment of the knowledge gaps and future research directions for researchers, encouraging investigators, stakeholders, and policymakers to make the best possible decision for food waste valorization.

The application of biochar in agriculture is a developing means to improve soil water retention, fertility, and crop yield. The present work focuses on biochar preparation from mixed vegetable and fruit wastes, using cauliflower, cabbage, banana peels, corn leaves, and corn cobs. The biochar produced at 400 °C was applied to the soil as an amendment to observe the qualitative changes of soil quality, plant growth, and water retention capacity of the soil based on screening in a previous study. Pot experiments were conducted at a laboratory scale having 0%, 2%, and 6% biochar mixed with sand. Each pot was sown with seeds of chickpeas (Cicer arietinum L.) and monitored over 60 days. Two biochar application rates improved soil quality by increasing soil porosity from 49.3 to ≥ 53.4%, more than doubling cation exchange capacity to ≥ 21.1 cmolc.kg⁻¹, providing a small reduction in bulk density of approximately 10% and decreasing electrical conductivity of the extract by at least 40% in comparison to control condition. The biochar application also increased key soil nutrients K, Mn, S, and P by a factor of 2–9 times. Application of biochar at 2% and 6% improved water retention from 55 to 77 and 91 mL respectively over the study and, more importantly, more than doubled the biomass yield for the same water application. The lower biochar application rate of 2% led to more germinated seeds (p = 0.0001), leaves (p = 0.0001), flowers, and fruiting chickpeas than the control condition. The 6% biochar application rate slightly improved plant height (p = 0.01) and provided a small reduction in water loss compared with the 2% biochar. Both biochar loadings increased the root and shoot biomass (p = 0.005) and nutrient content of the shoot and root biomass, particularly K, P, and S (p = 0.0001). This study demonstrates that biochar application at 2–6% is an effective means to increase chickpea yield and reduce water stress. Given small differences in performance within this application range, 2% application is recommended. The study establishes valorization of cellulose rich food waste in the form of biochar as a potential method for positive soil management and increased agricultural productivity in arid environments.

Green walls and roofs are sustainable building systems with several benefits. However, the irrigation requirements of these building systems conflict with water sustainability goals in water-scarce places. This study investigates using greywater directly to irrigate ornamental species for such situations by examining the effects of freshwater and greywater irrigation on Ruellia tuberosa growth, plant health and soil characteristics. Five replicates for each condition were grown for 91 days. Greywater irrigation led to a 15% higher plant growth height, a 31% higher plant biomass (p = 0.065), and a 71% increase in stem biomass (p < 0.001) compared to freshwater irrigation. However, greywater-irrigated plants had reduced chlorophyll content (10.7%, p < 0.001), and increased leaf chlorosis (p = 0.003), likely caused by stress from laundry and detergent chemicals. Greywater irrigation led to greater mineral content in greywater-irrigated plant biomass and soil for all minerals tested, most notably boron, which was deficient in the soil. Greywater-irrigated soil also had a higher organic content according to FTIR and electron dispersive spectroscopy. Greywater irrigation improved nutritional and soil conditions, including phosphate, which helped Ruellia tuberosa flourish. This study suggests raw greywater can replace freshwater in water-scarce climates for green wall irrigation instead of high-energy onsite greywater treatment systems.

Sustainable crop production supports food security by mitigating water and nutrient stress from manures by excessively drained water. Cow manure is a good nutrient resource to enhance soil fertility and plant growth but requires a suitable amender to reduce the nutrients loss by leaching. Worldwide more than 20,400 metric tonnes of pistachios were consumed where roughly 30% of the weight of the nut is the shell which could be a good feedstock for biochar production. Therefore, this study was conducted to produce biochar from pistachio shell by pyrolysis process at three different temperatures 350 to 550 °C and based on various properties characterization, the biochar at 450 °C was amended with 0% (control), 2%, 4% and 8% to the cow manure for eggplant growth (Solanum melongena). Out of all fractions of biochar application, 2% biochar has virtuous performance to increase 5.63 ± 1.45 cm of plant height, 1.33 ± 4.79 cm leaf length and 1.90 ± 4.43 cm leaf width over the control. The leaf chlorophyl content and plant biomass were also significantly (p = 0.02) increased compared to the control. The lower fraction of biochar application showed almost similar water retention capacity with control (p > 0.11) due to the better plant growth. Based on the findings of this study, it is proposed that lower fraction of biochar application with manure is a constructive solution to improve soil quality, reduce nutrient loss and eggplant growth. Under the circular economy and frameworks of sustainability, pistachio shell biochar production has a high legislative attention on valorizing nutshell wastes. Graphical Abstract

Biochar has received significant interest as a soil amendment but its relative performance to addition of high-quality soil is not well assessed. This study compared different loadings of cabbage-waste biochar produced at 360 °C against potting mixture (PM) as amendments to enhance basil (Ocimum basilicum) growth in sandy soil. Pot tests for six conditions of biochar, PM or their blend were tested at both 2% or 6% loading, plus a control, with soil and plant characteristics monitored. The combination of 6% biochar and 6% PM increased seed germination by 85% compared to the control, while 6% biochar applied in sandy soil reduced seed germination by 29%. However, significant benefits were realized later in the growing stage in comparison to the control and most other tested conditions. The 6% application of biochar to the soil enhanced leaf chlorophyll and carotenoid contents, membrane stability index, and leaf relative water content by 198%, 150%, 15%, and 5% over the control, respectively. The highest shoot and total biomass were achieved with the combined application of 6% biochar and PM, followed by 6% biochar only. When comparing only application of biochar or PM, biochar was the more favorable soil amendment at both 2% and 6% loadings. Biochar was also effective at enhancing plant uptake of beneficial nutrients, while immobilizing Al, which is detrimental, in the soil. Overall, biochar is a better soil amendment for sandy soil than equivalent quantities of PM, but mild benefits occur through their combined application.