With benefits to the human health, environment, economy, and energy, anaerobic digestion (AD) systems have attracted remarkable attention within the scientific community. Anaerobic digestion system is created from (bio)reactors to perform a series of bi-metabolism steps including hydrolysis/acidogenesis, acetogenesis, and methanogenesis. By considering the physical separation of the digestion steps above, AD systems can be classified into single-stage (all digestion steps in one reactor) and multi-stage (digestion steps in various reactors). Operation of the AD systems does not only depend on the type of digestion system but also relies on the interaction among growth factors (temperature, pH, and nutrients), the type of reactor, and operating parameters (retention time, organic loading rate). However, these interactions were often reviewed inadequately for the single-stage digestion systems. Therefore, this paper aims to provide a comprehensive review of both single-stage and multi-stage systems as well as the influence of the growth factors, operating conditions, and the type of reactor on them. From those points, the advantages, disadvantages, and application range of each system are well understood.

Municipal solid waste management is an environmental issue that has received considerable attention from researchers and environmental managers for decades. Supporting the management programs entail policies and regulations related to municipal solid waste. In developed countries, the implementation of environmental policies plays an important role and has a substantial impact on the effectiveness of solid waste management. However, in many developing countries such as Vietnam, the situation and effectiveness of the policy implementation have not been studied extensively. This investigation is conducted to ascertain the situation, limitations, and challenges in implementing solid waste management policy in Vietnam. Then, solutions for the problems and improvements for implementation efficiency are presented. This work used online questionnaires to survey environmental managers in different localities and applied qualitative research method to analyze data. The results show that not all national policies on solid waste management are implemented in all localities. Waste separation is also the foremost concern in municipal waste management in most localities of Vietnam. Most of the localities claimed that the unrealistic nature and difficult implementation of the policies and the lack of needed resources are the main limitations and challenges in Vietnam. Survey results also revealed that different localities in Vietnam have different solutions to increase policy implementation efficiency. Besides, the study also found similarities in the implementation of policies in solid waste management between Vietnam and some other countries and also gathered some valuable lessons for the improvement strategy. Finally, the implementation of an effective domestic solid waste management policy is an important platform for improving environmental quality and ensuring the sustainable development of the nation and mankind.

This study aims to present waste characterisation, solid waste management practice and analyse the challenges in the solid waste management system in the tourism destination of Hoi An City, Vietnam. The sampling and questionnaire surveys were conducted for measuring characterisation and management practice of solid waste. A material flow analysis method was used for analysing the waste flow. The results show that the tourism destination generated daily around 15080 kg t of waste, in which the significant proportions come from restaurants (46%), hotels (22%) and households (13%). The feature of the waste composition is high rates of kitchen waste (46.8%), tissue (11.54%) and recyclable materials (12.58%), which result in high moisture (46.79%) and a low heating value (16,866 kJ kg^-1) of waste. Also, solid waste management practices were evasively implemented by stakeholders with low rates and efficiency. Furthermore, a substantial gap of the solid waste management system is the confusion in waste collection activities, which is shown by the overload of waste in street bins and the financial loss for the solid waste management system owing to the non-compliance with collection regulation of stakeholders. Also, the mixing of waste by collection crews after separation at sources, the in-appropriation of collection time and manner are the dark points of the solid waste management system that may be causes of the non-cooperation of stakeholders. These gaps and confusion in the solid waste management system are the significant challenges in the improvement of the solid waste management system in the tourism destination toward sustainability.

The current study aims to analyze waste characteristics and management practices of the hotel industry in Hoi An, a tourism city in the center of Vietnam. Solid wastes from 120 hotels were sampled, the face-to-face interviews were conducted, and statistical methods were carried out to analyze the data. The results showed that the mean of waste generation rate of the hotels was 2.28 kg/guest/day and strongly correlated to internal influencing factors such as the capacity, the price of the room, garden, and level of restaurant. The differences in waste generation rate of the hotels were proved to be statistically significant. The higher the scale of hotels, the higher the waste generation rate. Moreover, the waste composition of the hotels was identified by 58.5% for biodegradable waste, 25.8% for recyclables and 15.7% for others. The relative differences in the waste composition of the hotels by climate, the features of hotels, and the types of the guest were explained. Whereby, the higher size of the hotels, the higher percentage of biodegradable and less proportion of recyclable waste. Also, this study revealed that the implementation status of waste management practices of the hoteliers initially reaped quite positive achievements with 76% for sorting, 39% for recycling, 29% for reduction, and 0.8% for composting. The rate of waste management practices was proportional to the scale of the hotel. This study provided information on waste management practice of hotel industry and contributed to the overall assessment of municipal solid waste management practices of Hoi An city.

A study to characterize municipal solid waste was carried out at various sources in Hoi An, a famous World Heritage City of Vietnam. The purpose of the research was to identify the generation rate and compositions of household waste from different types of areas of the city (rural, urban, and tourist quarters) as well as waste from tourism sources. The result will contribute to harmonized solid waste management for the city. Wastes from household, hotels, restaurants, and streets were collected daily in two weeks for generation and composition sampling. A stratified random sampling method was applied, and several statistical tools were carried out to analyze obtained data. As a result, the mean of household waste generation was 0.223 kg capita-1 day-1. The average waste generation per capita in the urban region, which included the city center-ST1 (0.203 kg capita-1 day-1) and the urban areas-ST2 (0.264 kg capita-1 day-1), was almost double that of the countryside-ST3 (0.12 kg capita-1 day-1). The difference was statistically significant. Waste from tourism sources may have a great contribution in the total amount of waste generation since tourist services are important and active activities in the city. The results of the study showed that hotels generated about 0.6 kg room-1 day-1 , one restaurant produced an average of 26.18 kg day-1 , and the mean of daily waste generation from tourist streets was 6.99 kg per 100 m per day. Degradable waste counted for more than half of municipal waste, and combustible waste (textile, leather, wood, diapers, etc.) had higher portions, which meant that biological and thermal treatment technologies could be potential options for the purpose of decreasing the amount of waste to landfill for the city.