New insights into nitrogen control strategies in sewage sludge pyrolysis toward environmental and economic sustainability.

Sewage sludge (SS) contains a certain amount of nitrogen (N), resulting in various content of N in the pyrolysis products. Investigates on how to control the generation of NH3 and HCN (deleterious gas-N species) or convert it to N2 and maximize transforming N in sewage sludge (SS-N) into potentially valuable N-containing products (such as char-N and/or liquid-N) are of great significance for SS management. Understanding the nitrogen migration and transformation (NMT) mechanisms in SS during the pyrolysis process is essential for investigating the aforementioned issues. Therefore, in this review, the N content and species in SS are summarized, and the influencing factors during the SS pyrolysis process (such as temperature, minerals, atmosphere, and heating rate) that affect NMT in char, gas, and liquid products are analyzed. Furthermore, N control strategies in SS pyrolysis products are proposed toward environmental and economic sustainability. Finally, the state-of-the-art of current research and future prospects are summarized, with a focus on the generation of value-added liquid-N and char-N products, while concurrently reducing NOx emission.

Initial ecological restoration assessment of an urban river in the subtropical region in China.

Rivers in urbanised cities are often polluted, black, and odorous, with poor water quality and deteriorated ecology. Despite many river restoration studies, assessments of ecological responses to river restoration practices remain scant. Benthic animals are useful biological indicators showing the change and succession of river ecosystems; however, previous studies have mainly focussed on a few target species without considering overall ecosystem integrity. Here, we used a multi-index biological assessment method, benthic index of biological integrity (B-IBI) to assess ecological responses to river restoration of the Shahe River in subtropical region of China. Spatiotemporal changes in the macrobenthos community structure after restoration were monitored to explore species succession. We found that the number of macrobenthos species increased from 16 to 42, with the emergence of some pollution-sensitive species during the restoration period. Molluscs showed widespread recovery, and their relative proportions almost doubled from 12.5% to 24.4%. Oligochaetes and chironomids were the pioneer species in the recovering communities, while gastropod molluscs and pollution-sensitive aquatic insects were transitional species that first settled during the initial recovery period. Based on our survey data, 25 candidate metrics were selected, and five core metrics (total taxa, Simpson diversity index, percentage of crustaceans and molluscs, percentage of predators, and percentage of collector-gatherers) were identified after screening to establish the B-IBI. Our analysis revealed a distinct improvement in the overall health of the river, with the proportions of "excellent" and "good" sites increasing from zero to 28.6% and from 14.3% to 42.9%, respectively. A correlation analysis indicated that water flow, molluscs, and total phosphorus content were the three drivers of ecological recovery in the Shahe River. Overall, our study demonstrates the importance of governance and restoration of rivers in tropical and subtropical cities, and provides valuable evidence that can guide the design and evaluation of river restoration works.