Investigation of Anaerobic Digestion of the Aqueous Phase from Hydrothermal Carbonization of Mixed Municipal Solid Waste

In 2017, the United States Environmental Protection Agency (EPA) reported that Americans generated over 268 million tons of municipal solid waste (MSW). The majority (52%) of this waste ends up in landfills, which are the third largest source of anthropogenic methane emissions. Improvements in terms of waste management and energy production could be solved by integrating MSW processing with hydrothermal carbonization (HTC) and anaerobic digestion (AD) for converting organic carbon of MSW to fuels. The objectives of this study were to (a) investigate HTC experiments at varying temperatures and residence times (b) evaluate aqueous phase and solids properties, and (c) perform AD bench scale bottle test on the aqueous phase. A mixture of different feedstock representing MSW was used. HTC at 280 °C and 10 min yielded the highest total organic carbon (TOC) of 8.16 g/L with biogas yields of 222 mL biogas/g TOC. Results showed that AD of the aqueous phase from a mixed MSW feedstock is feasible. The integrated approach shows organic carbon recovery of 58% (hydrochar and biogas). This study is the first of its kind to investigate varying temperature and times for a heterogeneous feedstock (mixed MSW), and specifically evaluating HTC MSW aqueous phase anaerobic biodegradability.

Making Biodegradable Seedling Pots from Textile and Paper Waste—Part B: Development and Evaluation of Seedling Pots

This study evaluates the efficacy of using textile waste blended with paper waste to form biodegradable seedling pots. A bio-composite blend of cotton (20% cotton, 40% newspaper, and 40% corrugated cardboard) and polycotton (20% polycotton, 40% newspaper, and 40% corrugated cardboard) with an optimum strength was formed into seedling pots. The appreciated seedling pots (untreated blends of cotton and polycotton) were compared with the commercial pots (cardboard seed starter pot and Jiffy pot) in terms of mechanical properties (tensile strength and compressive strength), biodegradability (soil burial test and anaerobic digestion), and seed germination. The untreated blends of cotton and polycotton pots demonstrated a comparable optimum strength, while the Jiffy pot and cardboard seed starter pot obtained the least tensile and compressive strengths, respectively. The anaerobic biodegradability assay suggests that the cotton blend pot, polycotton blend pot, and cardboard seed starter pot can degrade anaerobically because of high biogas and methane generation potential. A 100% seed germination was observed from the four seedling pots tested. Thus, the results demonstrate the efficacy of utilizing textile waste and paper waste to develop seedling pots with desirable strength and biodegradability compared to the commercial pots.

Anaerobic co-digestion of acerola (Malphigia emarginata) agro-industry effluent with domestic sewage at mesophilic and thermophilic conditions

This study evaluated the effect of temperature on the anaerobic co-digestion of West Indian Cherry agro-industry effluent (EAV) and domestic sewage (EDT). The assays were performed in triplicates of reactor flasks using treatments with different mixture compositions (T1=5%EDT+95%EAV;T2=20%EDT+80%EAV;T3=30%EDT+70%EAV) and anaerobic sludge as inoculum (5g.L-1), at mesophilic (35°C) and thermophilic (55°C) temperatures. The analyses of soluble chemical oxygen demand (DQOs) and volatile fatty acids (AGV) were performed by determining the removal efficiency of the DQOs, the decay rate constant of the DQO (Kd), and the percentages of anaerobic biodegradability (%BD) and methanation (%M). The inoculum biomass of the treatments was observed through scanning electron microscopy at the end of the degradation process (12 days). Regardless of the temperature, the anaerobic digestion was considered efficient, with biodegradability above 60%. The mesophilic temperature favored the anaerobic co-digestion for all mixture compositions, presenting more diversified and structured biomass at the end of the assays, as well as higher removal efficiencies of the DQOs and methanization, especially for T3 at 35°C (63% and 51%, respectively). Furthermore, the kinetics of the degradation process proved to be more accelerated at mesophilic conditions (Kd 0.1d-1) and in the treatments with a higher percentage of sewage (T2M and T3M).

Alkaline and acid solubilisation of waste activated sludge

The influence of acidic and alkaline conditions on the solubilisation process of waste activated sludge (WAS) was investigated using HCl and NaOH at pH 2, 10, 11 and 12. The rise in concentration of solubilised compounds, the influence of reaction time, and the influence of the concentration of total solids (TS) during the solubilisation process were determined. Physical and chemical tests demonstrated that pre-treatment provided a release of compounds from the sludge floc matrix into the soluble fraction, characterising the solubilisation process. The highest degree of WAS solubilisation was observed when a pH of 12 was applied. Although largest effects were already attained after 0.25 h, WAS solubilisation continued reaching an increase in total dissolved solids by a factor 10.4 after 720 hrs. Under these conditions, the dissolved organic carbon (DOC), proteins, and carbohydrates resulted in releases up to 15, 40 and 41 times, respectively; and phosphorus increased 5.7 times. Results indicate that by applying alkaline pre-treatment, higher TS concentrations can be treated per reactor volume compared to non-pre-treated WAS. Aerobic and anaerobic biodegradability tests showed increased bioconversion potentials in full-scale treatment plants. The respirometry tests ratify the improvement in solubilisation, with O2 consumption rates increasing 1.4 times, concomitant with an additional 261 mg·L−1 of the COD used, which represents 90% bioconversion of waste activated sludge. Biomethanisation test indicated an increase of 3.6 times relative to the blank.