Humic substances (HSs) occupy 80% of organic matter in soil and have been widely applied for soil remediation agents, potential battery materials, and adsorbents. Since the HS extraction rate is very low by microbial degradation in nature, artificial humification processes such as aerobic composting (AC) and hydrothermal treatment (HT) have attracted a great deal of attention as the most important strategies in HS production. This article aims to provide a state-of-the-art review on the development of conversion of biomass waste into HSs based on AC and HT for the first time in terms of mechanisms, characteristics of HSs’ molecular structure, and influencing factors. In addition, some differences based on the aforementioned information between AC and HT are reviewed and discussed in the conversion of biomass waste into HSs in a pioneering way. For biomass waste conversion, a feasible strategy on effective humification processes by combining AC with HT is proposed.

With the simultaneous increase in wastewater generation and wastewater treatment rates in China, the annual production of residual sewage sludge (RSS) has been steadily rising, exceeding 70 million tons with an 80% moisture content. The sustainable resource utilization of RSS will be the predominant disposal method instead of sanitary landfilling in China. This review aimed to systematically analyze the major sustainable resource utilization technologies for RSS. Firstly, the basic characteristics of RSS in China were analyzed. A comparative analysis was conducted to assess the advantages, disadvantages, and applicability of three primary sustainable resource utilization technologies for RSS: building materials, energy utilization, and phosphorus recovery, aiming to provide clear insights for the development of future strategies. The research findings revealed that no single method can economically and environmentally address all challenges in the utilization of RSS resources. It is necessary to adopt appropriate resource utilization technologies according to the characteristics of RSS from wastewater treatment, achieving integration of pollution control and resource utilization. This review can provide scientific guidance for future sustainable utilization of RSS resources.