Increasing regulations diverting organic waste from landfills require the replacement of old waste management infrastructure. Since there are several organics diversion options, including anaerobic digestion, composting, and pyrolysis, a multi-objective optimization approach was used to evaluate environmental, economic, and social impacts and identify the most sustainable option for 11 waste compositions that represent different regions and economic sectors. Impacts were quantified using life cycle assessment and costing methodologies and by monetizing social externalities associated with life cycle gaseous emissions. Preliminary results show that no organics diversion option simultaneously minimized environmental, economic, and social impacts for any waste composition. For example, for the food-focused composition, anaerobic digestion minimized environmental impacts but had large economic impacts (e.g., costs were three times the cost of composting). For the yard-focused composition, pyrolysis minimized both social and environmental impacts but cost twice as much as composting; pyrolysis could be an optimal solution if the resulting biochar could be sold at a price that was 5.6 times higher than existing compost prices or if carbon were taxed at a rate 28 times larger than existing rates. Breakeven analyses were also conducted with other policy options and waste compositions to identify additional opportunities where all three sustainability objectives could be minimized. For a single objective: pyrolysis was environmentally preferred for compositions with limited food waste amounts; composting or pyrolysis were often socially preferred; and composting was always the least expensive. Overall, this work will help inform how to sustainably implement new infrastructure and respond to changing regulations.

A novel four-chamber electrochemical membrane system (EMS) was developed to recover phosphorus and nitrogen from digester centrate, by synergistically coupling water electrodialysis with membrane contactor. Nitrogen was separated sequentially under electric field as NH₄⁺, and through gas permeable membrane as NH₃ due to the in-situ production of hydroxide in the cathode of EMS. While phosphorus was transported through the anion exchange membrane together with other anions under electric filed and combined with in-situ protons generated from the anode of EMS, which can be used as partial of the acid absorption solution to recover NH₃. This system could achieve 95% and 85% recovery efficiency for NH₄⁺-N and PO₄^3--P with specific energy consumption of 8.2 ± 0.2 kWh kg^-1 N and 178.0 ± 10.6 kWh kg^-1 P. With low heavy metals being detected in the recovery solution (Cu<0.2 mg L^-1 and Ni<0.05 mg L^-1, decreasing from 10 mg L^-1 and 10 mg L^-1 in the digester centrate, respectively), the recovered solution could be used as liquid fertilizer after dilution and pH adjustment, or used to form solid fertilizer struvite. Additionally, 0.74 mgCu kg^-1 and 0.38 mgNi kg^-1 was detected in the struvite, significantly decreased from 48.5 mgCu kg^-1 and 62.1 mgNi kg^-1 if struvite was directly recovered from digester centrate. This study has demonstrated the feasibility of a four-chamber EMS for successfully recovery of both nitrogen and phosphorus from digester centrate. The results would encourage further exploration of the EMS in terms of reduced energy consumption and enhanced transport of target ions.

There is an urgent need to re-balance the global nitrogen cycle and reduce greenhouse gas emissions associated with industrial fertilizer use. One strategy is to produce fertilizers by recovering nutrients from human urine. Using columns packed with cation exchange resin, ammonium (NH₄⁺) from urine can be captured and subsequently concentrated via elution to generate a concentrated liquid fertilizer. The main objective of this study was to investigate the performance of different eluents. In particular, we investigated three different eluents at equinormal concentrations: sulfuric acid (1 M H₂SO₄, strong acid), sodium hydroxide (2 M NaOH, strong based), or sodium sulfate (1 M Na₂SO₄, salt). Two major parameters were evaluated i.e., stoichiometric efficiency of the eluent and concentration factor of nitrogen in the liquid fertilizer. The calculated stoichiometric efficiencies after passing 6 bed volumes of 1 M H₂SO₄, 2 M NaOH, or 1 M Na₂SO₄ were 0.58, 0.86, 0.51, respectively. The achieved concentration factor of nitrogen in the final liquid fertilizer was 1.64, 1.92, 1.51, using 1 M H₂SO₄, 2 M NaOH, and 1 M Na₂SO₄, respectively. Highest stoichiometric efficiency and concentration factor for 2 M NaOH was attributed to two concurrent reactions occurring in the columns: an ion-exchange reaction between Na⁺ and adsorbed NH₄⁺ and acid-base reaction between OH^– and NH₄⁺. Both these reactions promoted the desorption of ammonium from the cation-exchange resin. The findings from this study highlights a strategy of maximizing chemical use efficiency and the nutrient density of the final fertilizer product.

Phosphorus (P) is an essential, limited resource for the maintenance of the global food supply. However, P in runoff from farmlands and discharges from wastewater treatment plants can lead to eutrophication and the growth of harmful algal blooms. Multiple studies have consistently shown that metal cations (e.g., Al²⁺, La³⁺, Fe³⁺, Mg²⁺) exhibit great potential for P-capture. For this reason, metal (hydr)oxide materials are one exemplary class for commercial and industrial use for P-recovery. In this systematic study, we investigate the underlying mechanism of phosphate capture for metal oxides (MO), and how these mechanisms relate to MO composition and structure. Theoretical results from density functional theory provide the basis for evaluating MOs containing Fe³⁺, La³⁺, and Al³⁺. To evaluate the rate and extent of P-capture, batch immersion experiments were completed with MOs in both synthetic and natural phosphate-containing solutions, and the effects of P/MO molar ratio and solution pH were investigated. Aqueous solutions were analyzed for P using Colorimetric methods, and sorbed P-concentrations were determined via mass balance. Prior to immersion, zeta potential, particle size distribution and BET specific surface area of the materials are measured. X-ray Diffraction, Scanning Transmission Electron Microscopy, and Energy-Dispersive Spectroscopy were used to characterize the materials before and after contact with P-solutions, which helps to inform sorption mechanism determination. Additionally, batch desorption was performed to assess the potential for P-recovery for each material. We find that La³⁺ shows exceptional phosphate sorption in comparison to the other metal cations, because of its high affinity for P.

Whole digestate, a slurry produced from anaerobic digestion of wastewater sludge, is enriched with reactive PO₄^3- that is suitable for phosphorus (P) recovery. Current P recovery approach is economically prohibitive because of a high chemical and energy consumption. This study proposes an electro P leaching and precipitation process (EPLP) that eliminates chemical addition by leveraging native Ca²⁺. The EPLP achieved high P leaching efficiency of 93.3% in the anode and 99.5% of PO₄^3--P precipitation in the cathode, primarily forming calcium phosphate. This process was energy-efficient with a consumption of 82.87 kWh kg^-1 P, one of the lowest among literatures. Mass balance analysis showed that 73.8% to 92.6% of P was converted into two harvestable forms: suspended solids in the cathodic effluent and immobilized P inside the cathode chamber. Solids collected from the effluent had high P content of 28.42~33.51% as P₂O₅, suitable for high-grade phosphate rock. The presence of heavy metals in the P product was alleviated under a higher current density of 20 to 30 A m^-2. Long-term operation demonstrated that periodic acid wash enabled normal operation for 10 to 11 cycles and harvested 1805.8 mg L^-1 PO₄^3--P after three reuses. The EPLP provided additional benefits, including improved dewaterability of the whole digestate and opportunities for ammonia nitrogen recovery. The EPLP is a promising solution for efficient and chemical-free P recovery from municipal solid waste.