Worldwide Research Progress and Trend in Sludge Treatment and Disposal: A Bibliometric Analysis

As a byproduct of sewage treatment in wastewater treatment plants, sludge has dual attributes with pollution and resource, and its research is important to ecological environment and energy security. Therefore, it is of great significance to analyze and summarize the development of research in the field of sludge treatment and disposal. Based on a bibliometric analysis, this paper analyzed the worldwide research process and trend of sludge treatment and disposal among 49,300 research articles and reviews from 1975 to 2021, which were divided into six time periods for a more detailed analysis. In this analysis, countries, institutions, authors, and keywords were discussed respectively through visual maps. The United States (before 2007–2011) and China (after 2007–2011) were the countries that published the most papers, and cooperation between China and other countries became more frequent after 2007–2011. Research institutions and authors from developed countries and China accounted for the largest proportion. As the main research objects, activated sludge and sewage sludge appeared most frequently in keywords analysis. In terms of the overall trend, sludge treatment and disposal gradually developed from harmless treatment and reduction of sludge to the control of emerging pollutants, recycling of sludge and multidisciplinary research. The analysis of cited authors (W. W. Eckenfelder, M. Henze, and Y. Liu) reflected the recognition of worldwide researchers. The top 10 cited journals were classified as Q1 and Q2 according to journal citation reports, and they were favored by researchers.