Starting up anammox system with high efficiency nitrogen removal at low temperatures: Performance optimization, sludge characterization and microbial community analysis.

Anaerobic ammonia oxidation (anammox) has potential advantages for nitrogen removal when operating at medium temperatures, but the increased operation costs of heating limit its application. It would be advantageous to start and operate anammox at low temperatures, the feasibility of which was studied here on a lab scale. Two identical expanded granular sludge bed (EGSB) reactors were inoculated at 35 ± 1 °C (Amed) and 15 ± 3 °C (Alow). Results showed that anammox was successful after 138 d for Alow, only 7 d longer than Amed. Stable operation to 194 d in Alow, the nitrogen loading rate (NLR) increased to 1.01 kg m-3·d-1, giving a high nitrogen removal efficiency (NRE) of 85%, which was only slightly lower than that of Amed (90%). More extracellular polymeric substance (EPS) was produced by the microbes of Alow compared to Amed, which prevented anaerobic ammonia oxidizing bacteria (AnAOB) against low temperature stress. Microbial community revealed presence of Candidatus Jettenia in Amed with relative abundance 7.4%, while the "cold-tolerant" Candidatus Kuenenia with 4% was the dominant anammox bacteria in Alow. The anammox granules adapted well to low temperatures and demonstrated high efficiency in anammox process without heating. Therefore, constructing an energy-saving and cost-effective anammox system in high latitudes or high altitudes can be considered.

Treatment of high-concentration phosphorus wastewater based on foamed concrete.

Phosphorus is a nonrenewable resource, and the recovery of phosphorus from wastewater containing high concentrations of phosphorus is of great importance. In this work, a novel method for highly efficient treatment of high-concentration phosphorus-containing wastewater (50 mg/L, 100 mg/L and 150 mg/L) with low energy consumption was developed by using the block waste foam concrete (FC) as a potential phosphorus recovery material. The results showed that acid leaching significantly improved the accumulation efficiency of phosphorus in calcium hydroxyphosphate (HAP) via accelerating the release of calcium in wastewater. The recovery rate of phosphorus could reach 99.0% under the pH value of 9.0 at 25 °C, using 2.0 g FC. It was also found that the microporous structure of the surface of FC provided the adsorption sites for phosphorus, resulting in the adsorption rate in different concentrations of phosphorus-containing wastewater up to 14.5%. It indicated that FC achieved the recovery of phosphorus from high-concentration phosphorus-containing wastewater by coupling HAP crystallization and physical adsorption to polyphosphorus.