Anaerobic digestion (AD) is an effective approach to recovering chemical (organic) energy from excess sludge, but the conversion efficiency for energy is usually not very high. One of the obstacles comes from the severe inhibition of humic acid (HA) on both hydrolytic and methanogenic process on the AD. Therefore, it is necessary to ascertain some effective approaches to relieving the inhibition of HA for obtaining a high methane (CH₄) yield. With the “clean” sludge (cultured by synthetic wastewater) containing almost no HA and metal ions, the inhibition of HA on the AD process was designed by dosing HA at 15% VSS, and relieving the inhibition by metal ions was also designed by dosing the different amounts of Ca²⁺ and Al³⁺. Based on the batch AD experiments, solo Ca²⁺=100 mg /L or Al³⁺=70 mg/L added realized the highest relieved efficiency of 65%, respectively. Interestingly, dual metal ions added at the low concentrations (Ca²⁺=50 mg/L and Al³⁺=10 mg/L) could reach up to 80 % of the relieved efficiency, which was attributed to the synergistic effect of 1+1>2. The mechanisms behind the phenomena could be that metal ions might interact with HA via electrostatic force, cation exchange and sweep flocculation. Thus, some key hydrolytic and methanogenic enzymes could indirectly be reactivated and degradation of organic substances could be enhanced in the AD process. In wastewater treatment plants, metal ions contained in excess sludge would “inherently” relieve the inhibition of HA to an extent, which depends on the effective and/or optimal concentration of metal ions at a free (unabsorbed and/or unwrapped) state.

To better face the challenges of rapid urbanisation, it is recommended urban heritage management is carried out through community participation. In the Chinese context of state centralisation, however, inclusive participatory governance for urban heritage has remained limited, and effective ways of engaging residents in decision-making have yet to be explored adequately. This paper aims to explore community participation within Chinese urban heritage management, taking the Old Town of Lijiang as a case study. During fieldwork, in-depth semi-structured interviews were carried out with both native and migrant residents as well as administrators. Based on a community participation assessment framework, the interview guide was developed and then built on four aspects: community participation in decision-making; the competence of participants; the right to social justice and confidence of participants; and community empowerment and equity. This paper reveals the current state of participatory practices in the Old Town of Lijiang and, specifically, discusses the roles of residents, elites and community-based organisations in decision-making concerning urban heritage management, in the contexts of state-centralisation. Chinese urban heritage management needs to raise public awareness and willingness as well as give residents more responsibilities and power to face the challenges of rapid urbanisation, but currently, the degree of participation is still minimal, only between informing and consulting.

Community participation is an essential issue in heritage management. The international heritage organisation ICCROM published a guidance document discussing people-centred approaches to heritage management in 2015. Cultural heritage management is recommended to be carried out through a community participation process. Despite the growing literature on community participation in cultural heritage management, little research has been done on comparing Chinese to international approaches. Although in China several pilot projects have conducted effective community participation and achieved excellent outcomes. This paper aims to fill this gap by providing an overview that compares and discusses the similarities and differences between Chinese and international approaches. A systematic literature review of the state-of-the-art was conducted to explore these differences based on four themes: engaged communities, participatory methods, degrees of participation and steps taken within cultural heritage management. This review concludes both Chinese and international practices seek to collaborate with and empower local communities in their approaches, with Chinese pilot cases, such as Tianzifang in Shanghai. However, in general, Chinese cultural heritage management is government-led, in which community participation is happening to a minimal degree. China is encouraged to learn from international practices when developing contextualised management approaches, to better face the challenges of rapid urbanisation.

Community participation is a key part of heritage management. However, in practice, unlike natural heritage, the nature of community participation within cultural heritage is seldom assessed, nor are there theoretical frameworks developed to baseline such assessments. To fill this knowledge gap, this paper developed and tested an assessment framework, to assess community participation within cultural heritage. Based on the conceptualisation of community participation from heritage management policies, a literature review was conducted to develop an assessment framework, including four criteria and 23 indicators. This assessment framework was tested on the management practices of 36 Chinese cultural heritage properties inscribed on the UNESCO World Heritage List from 1987 to 2018. Using content analysis as a method, this research applied this assessment framework to UNESCO documents, reporting on the state-of-the-practice of heritage management as applied to Chinese World Heritage. The results provide an overview of the current situation on how community participation is positioned within World Heritage management in China. Several World Heritage properties in China have reported relatively high community participation in examples such as Honghe Hani Rice Terraces and Kulangsu. However, most of them demonstrate minimal community participation, such as the Yungang Grottoes and Lushan National Park. Moreover, the assessment framework of community participation in heritage management has been extended and improved, which is relevant to heritage management practices worldwide.

Handling excess sludge produced by wastewater treatment is a common problem worldwide. Due to limited space available in landfills, as well as difficulties involved in using excess sludge in agriculture, there is a need for alternative disposal methods. Although anaerobic digestion (AD) is widely used in processing sludge, only partial energy recovery from methane and sludge volume reduction can be achieved, resulting in a substantial amount of sludge remaining, which needs to be disposed of. Direct incineration after sludge drying is one possible option, a practice that is already in place in some cities in China. A comparison between direct incineration and conventional AD (with or without pretreatment by thermal hydrolysis) has to be made with respect to the energy balance and investment & operational (I & O) costs. This comparison reveals direct incineration to have the lowest energy deficit and I & O costs. Therefore, it is expected that direct incineration without AD will become the preferred sustainable approach to handling sludge.

In dealing with wastewater, chemical energy has traditionally been perceived as the only source of recoverable energy in moving towards the carbon-neutral operation of wastewater treatment plants. Based on an estimation of practically recoverable energy embedded in municipal wastewater, however, the potential for thermal energy (90% recovery from wastewater) is much higher than for chemical energy (COD, 10% recovery). The carrier of chemical energy (COD) has a high exergy value which should, from a sustainability point of view, be utilized to the greatest extent possible. Rather than being converted into methane (and subsequently into carbon dioxide), carbon (COD) contained in wastewater should be converted into highly valuable organic products. Thermal energy could be utilized for district heating/cooling, agricultural greenhouses, and even for drying dewatered sludge. In this way, thermal energy can indirectly offset the energy demand for wastewater treatment. The limitations in utilizing thermal energy are not generally based on technical difficulties; in fact, they can be mainly attributed to supply distances and governmental policies. It would, therefore, be greatly beneficial if municipal authorities would work together to jointly plan utilization of this thermal energy.

Inhibition by humic substances (HSs) on anaerobic digestion of excess activated sludge is one of the limitations for converting more organics into biogas. In order to counteract the inhibition from HSs, the present study was initiated to understand the dynamic changes (content and structure) of HSs during the anaerobic digestion of synthetic and real sludge. For the first time, the present work studied the dynamics of HSs separately in the liquid and solid phases. These observations on HSs conversions by potentiometric titration, UV–Vis, FTIR, and two-dimensional infrared spectra, confirmed that the dynamic changes of HA and FA compositions were caused by losing aliphatic moieties and enriching aromatic moieties in the structural compositions. This changes increased the humification degree, aromaticity, and the amounts of oxygen-containing functional groups. Based on the observations, strategies to alleviate the inhibition effect were discussed.

Anaerobic digestion (AD) is a technology for recovering chemical energy as methane from excess sludge/waste. Unfortunately, humic acids (HA) contained in excess sludge can have the effects of inhibiting the efficiency of energy conversion. Based on a batch experiment, the impact of HA on a semi-continuous AD process was sequentially investigated, with the impact on the associated enzymes and microorganisms being measured. The results of this semi-continuous experiment indicate that the inhibition of the microbial community increased with an increased HA:VSS ratio. Long-term cultivation did not result in the adaption of methane production to the presence of HA. Moreover, at HA:VSS = 20%, the strongest inhibition (74.3%) on energy conversion efficiency was observed in the semi-continuous experiment, which was two-fold higher than that recorded in the batch experiment. This is attributed to serious and irreversible inhibition of both acidogenic and methanogenic microorganisms, as well as the physical-chemical reactions between HA and the associated enzymes which, it was concluded, were the dominant mechanisms of inhibition in the batch experiment.

The Paris Climate Treaty implies the coming of a new era towards carbon-neutral operation in wastewater treatment plants (WWTPs), and thus energy self-sufficiency from biosolids and/or heat in the form of wastewater temperature has to be considered. In this regard, anaerobic digestion (AD) of sludge should be paid renewed attention to resolve a low conversion efficiency of biosolids. As a potential way to energy positive operation, exogenous iron has been proposed to enhance methane production in recent years. In this review, the authors provided a deep insight into the feasibility of iron-enhanced AD system. Hydrogen evolution from iron corrosion and its effects on CH₄ production is firstly reviewed; then the roles of iron in reducing ORP was illustrated with regard to its impact on fermentation type; serving as an essential element and potential electron donor, the stimulating effects of iron on microorganisms and enzyme activities were also elaborated, and thus the technical feasibility of iron-based AD could be evaluated. In regards of the environmental and economic impacts of iron-based AD, life cycle assessment (LCA) was employed to calculate its economic feasibility, and the results revealed that iron-based AD system could reduce both operational costs and carbon emissions. Conclusion was drawn that iron-based anaerobic digestion is promising on technical level as well as economic perspective, and is expected to contribute to carbon-neutral operation of WWTPs. Iron-based anaerobic digestion is such a promising and sustainable strategy towards circular economy that it could be applied to many cross-disciplinary fields.