Beneficial reuse of drinking water treatment plant residues (WTRs) has been intensively studied worldwide in the last decades, but few engineering applications can be found. The majority of WTRs were directly reused in cake form (after dewatering), e.g., alum sludge cake as main substrate used in constructed wetlands (CWs), or oven dried and ground powdery form, e.g., sorbent for pollutant removal. However, WTRs reuse in such forms has several drawbacks, i.e., difficulty of recovering and easy clogging (in CWs), which result in limited WTRs engineering applications. Granulation or pelleting could widen and be a wiser WTRs reuse route and also seems to be a promising strategy to overcome the “application bottleneck” issues. In the literature, a number of trials of WTRs granulation have been reported since 2008, including sintering ceramsite, gel entrapment and newly emerged techniques. Hence, there is a need to overlook these studies and promote WTRs granulation for further development. To this end, this review firstly provides a piece of updated comprehensive information and critical analysis regarding WTRs granulation/pelleting technology. It aims to enhance WTRs granulation studies in the developing stage and thus enlarge WTRs engineering applications.

Cities in plain areas have small slopes at the bottoms of rivers, with weak hydrodynamics, heavy pollution and poor self-purification capacities for the restoration of biological habitats. Hydrodynamic and water quality improvements are effective means for the ecological restoration of plain urban rivers. The potential for fish habitat resilience in a typical urban river network plain (more than 130 river sections) in the Dianbei part of China was studied. The tolerant fish, Carassius auratus (C. auratus), and the sensitive fishes Trachidermus fasciatus (T. fasciatus) and Anguilla japonica (A. japonica), were selected as the protection targets, and hydrodynamic factors, river morphology and water quality factors were chosen as environmental indicators. With the fish habitat suitability index, a fish habitat resilience potential evaluation model was established. The response of the habitat resilience potential index (HRPI) to hydrodynamic regulation was subsequently analyzed, and the HRPI indicated an increased habitat resilience potential with its value increasing from 0 to 1. Overall, the resilience potential of tolerant fish species was greater than that of sensitive species in the Dianbei. For the HRPI of C. auratus adults (tolerant species), approximately 62.8% of the river sections were above 0.6 (high resilience level) and were concentrated in the northwest area of the river network. While for the resilience potential of A. japonica adults and T. fasciatus adults (sensitive species), only 60% of the river sections exhibited moderate resilience level (HRPI > 0.5). The average dimensionless habitat resilience potential index (AHRPI) was enhanced by water diversion with its values increased by 10.3%, 9.3% and 12.7% for C. auratus adults, T. fasciatus adults and A. japonica adults, respectively. The habitat resilience potential of C. auratus changed little during the spawning period, which indicated that the effect of hydrodynamic regulation was limited. This study provides a scientific basis for managers to restore urban river network habitats in plain areas.