Biochar holds promise as a soil amendment with potential to sequester carbon, improve soil fertility, adsorb organic pollutants, stimulate soil microbial activities, and improve crop yield. We used a hardwood biochar to assess its impact on corn (Zea mays) grain, biomass yields and greenhouse gas emission in central Kentucky, USA. Six treatments included as follows: control (C) with no amendment applied; poultry litter (PL); biochar (B); biochar + poultry litter (B + PL); fertilizers N-P-K (F); and biochar + fertilizers (B + F). Biochar was applied only once to plots in 2010 followed by rototilling all plots. Only PL and fertilizer were applied annually. When applied alone, biochar did not significantly increase dry matter, grain yield, and N-P-K uptake. There was also no significant difference between the combined treatments when compared with PL or F applications alone. We observed a slight increasing trend in corn grain yield in the following 2 years compared to the first year from biochar treatment. Poultry litter treatment produced significantly greater N₂O and CO₂ emissions, but emissions were lower from the B+PL treatment. We conclude that this biochar did not improve corn productivity in the short term but has potential to increase yield in the long term and may have some benefit when combined with PL or F in reducing N₂O and CO₂ emissions.

Increasing the efficiency of anaerobic digesters and improving sludge breakdown is vital to reducing the cost of biogas production and reducing the environmental consequences of sludge disposal. The performance of two unheated anaerobic digestion systems, one exposed to sound at <20 kHz by waterproofed speakers and one acting as a control, were compared for over a year. The digester systems were both composed of primary (11.4 m³) and secondary (3.8 m³) anaerobic tanks, facultative tertiary (3.0 m³) tanks and an aerobic holding tank from which effluent was mixed with feed and recirculated back to the system. Exposure of the gas saturated digestate to a low frequency sine wave induced numerous bubble harmonics up to, and presumably beyond, ultrasonic range, showing that sonification of a highly gaseous liquid might be used to accomplish low power ultrasonication of digestate at greater distances than is possible with conventional ultrasonic technology. Through the summer of 2019, the sound-treated system produced 27% more biogas than the control system, and 74 times more during the winter when biogas production by the control systems essentially ceased. Afterwards, the control system produced more biogas due to depletion of volatile solids in the sound-treated digester. Results show that sound can be used for faster digester startup and substitute for a share of heating requirements during cool months.

Confined animal feeding operations often use pit recharge waste management systems, where water is recycled from treatment lagoons to flush waste from animal housing. This practice has been linked to reduced animal performance and excess mortality due to the presence of pathogens and ammonia. As a project to improve the quality of flush water, the effluents from two anaerobic digesters were treated in aeration–recirculation systems, one inoculated with an anammox (anaerobic ammonia oxidation) consortium and the other left uninoculated. The effluent from the aeration tanks was sent to a shared constructed wetland planted with cattails and duckweed and hence to a lagoon. Water from the lagoon was recycled back to the digesters, where it was reused to suspend waste for anaerobic digestion. Fresh water was used to suspend feed to the system for the first six months, whereas lagoon water was recycled into the system for the last year and a half. The inoculated aeration tank reduced ammonium concentrations more efficiently than the uninoculated tank and also performed nitrification more effectively. Ammonia oxidation and denitrification continued in the wetland and the lagoon, and ammonium concentrations in the recycled water were reduced by over 98 percent compared to its concentration in the digesters. Phosphate concentrations in the lagoon averaged only 5 percent that of its concentration in the digesters over the two-year evaluation period. Inductively coupled plasma spectroscopy of wastewater sludge and plants showed that chemical precipitation of phosphate and utilization by duckweed and cattails accounted for phosphorus reduction by the system. Wastewater pH, conductivity, chemical oxygen demand and oxidation reduction potential were steady during the study period.