Sheng Li

Bio: Sheng Li is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Fouling & Forward osmosis. The author has an hindex of 23, co-authored 53 publications receiving 1251 citations. Previous affiliations of Sheng Li include Delft University of Technology & Center for Excellence in Education.

Pyrosequencing Reveals Bacterial Communities in Unchlorinated Drinking Water Distribution System: An Integral Study of Bulk Water, Suspended Solids, Loose Deposits, and Pipe Wall Biofilm

Abstract: The current understanding of drinking water distribution system (DWDS) microbiology is limited to pipe wall biofilm and bulk water; the contributions of particle-associated bacteria (from suspended solids and loose deposits) have long been neglected. Analyzing the composition and correlation of bacterial communities from different phases helped us to locate where most of the bacteria are and understand the interactions among these phases. In the present study, the bacteria from four critical phases of an unchlorinated DWDS, including bulk water, pipe wall biofilm, suspended solids, and loose deposits, were quantified and identified by adenosine triphosphate analysis and pyrosequencing, respectively. The results showed that the bulk water bacteria (including the contribution of suspended solids) contributed less than 2% of the total bacteria. The bacteria associated with loose deposits and pipe wall biofilm that accumulated in the DWDS accounted for over 98% of the total bacteria, and the contributions of bacteria in loose deposits and pipe wall biofilm were comparable. Depending on the amount of loose deposits, its contribution can be 7-fold higher than the pipe wall biofilm. Pyrosequencing revealed relatively stable bacterial communities in bulk water, pipe wall biofilm, and suspended solids throughout the distribution system; however, the communities present in loose deposits were dependent on the amount of loose deposits locally. Bacteria within the phases of suspended solids, loose deposits, and pipe wall biofilm were similar in phylogenetic composition. The bulk water bacteria (dominated by Polaromonas spp.) were clearly different from the bacteria from the other three phases (dominated by Sphingomonas spp.). This study highlighted that the integral DWDS ecology should include contributions from all of the four phases, especially the bacteria harbored by loose deposits. The accumulation of loose deposits and the aging process create variable microenvironments inside loose deposits structures for bacteria to grow. Moreover, loose deposits protect the associated bacteria from disinfectants, and due to their mobility, the associated bacteria reach taps easily.

Fouling and cleaning of ultrafiltration membranes: A review

Abstract: Ultrafiltration (UF) is one of the best options for both one-stage and as part of multi-stage water and wastewater purification. This review summarises the known facts about the fouling processes and cleaning procedures and details of the most successful physical and chemical cleaning combinations. The optimum cleaning is closely linked to the nature of the fouling. Precise knowledge of both the fouling type (organic, inorganic, or biological) and the fouling mechanism (gel formation, adsorption, deposition, pore blockage, or cake formation) is the key to success in UF membrane cleaning.

Ecosystems and Human Well-Being

Abstract: Over the past 50 years, humans have altered their environment to a significant extent, although human well-being is dependent on ecosystem functioning. Ecosystems are particularly affected by unsustainable use of resources, such as, food, water, and timber. Ecosystem functions depend on water, carbon, and other nutrients cycles. Human activities have modified these cycles in a number of way. Use of ecosystems for recreation, spiritual enrichment, cultural purposes, and for other short term benefits is growing continuously, although ecosystem capacity to provide such services has reported to be declined significantly. Human well-being depends on material welfare, health, good social relations, security and freedom, which are affected by changes in ecosystem services. Intensive ecosystem use often produces short-term advantage. Poverty level remains high in more than one billion people, who are dependent on ecosystems with an income of less than $1 per day as reported elsewhere. Regions including some parts of Africa, Asia and Latin America have the greatest ecosystemrelated problems and are facing developmental challenges. Habitat change occurs, for instance, when the area of land used for agriculture or cities is expanded. Instability and unproductivity including desertification, water logging, mineralization and many other unwanted outcomes throughout the world are continuing. Habitat fragmentation by roads, canals, power lines limits the species potential for dispersal and colonization. Indirect drivers, like changes in human population, economic activity and technology as well as socio-political and cultural factors affect ecosystems by influencing direct drivers. World climate has changed and continues to change, affecting temperature, rainfall and sea levels. Intensive fertilizer use has polluted ecosystems. Climate change and high nutrient levels in water are becoming increasing problems. Ecosystem management for shortterm benefits is increasing. Loss of biodiversity makes it difficult for ecosystems to recover from damage. Once an ecosystem has undergone an abrupt change, recovery to the original state is slow, costly, and sometimes impossible. Changes in ecosystems complexity- functioning relationships could diminish the stability, resistance and resilience of managed terrestrial ecosystems, and may jeopardize important food and fibre sources, and ability of natural ecosystems both to provide natural resources, and to remove pollutants from atmosphere. Ecological complexity and ecosystem functioning depend on factors that govern species coexistence. Complexity of landscapes is determined by number of ecosystem types, their characteristics, their sizes and shapes, and associated connectivity. Complexity at this scale would have large consequences on regional to global scale processes. Presence and arrangement of keystone ecosystem types, such as, wetlands often determine total carbon and nitrogen balance of a region. Changes in average or extreme environmental events and intense land use management are believed to increase species extinction rate in isolated habitat fragments. Loss of key species, such as, top predators, fruit dispersers and pollinators from habitat may severely disrupt ecosystems functioning. Land use changes due to expanding urbanization, concomitant landscape fragmentation and intensification of production systems. Such change results in transformation of an ecosystem, form one state to another state, via a transition phase. The combined value of 17 ecosystem services has been reported in the estimated range of US$16-54 trillion per year by Costanza and others. About 30% of modern medicines are developed from plants and animals, and 10 of the world's 25 topselling drugs in 1997 were reported to be derived from natural sources. Global market value of pharmaceuticals derived from genetic resources is estimated at US $ 75 000-150 000 million annually. Some 75% of the world's populations rely for health care on traditional medicines, which are derived directly from natural sources as recorded elsewhere. Socio-economic development of human civilization and human well-being depends on long-term health of environment including ecosystems. Environmental problems are generally addressed in isolation, but practically such problems are interrelated, and originate from the root cause of unsustainable development. Damage to natural ecosystems and release of environmental pollutants must be minimized for protecting natural ecosystem, and human well-being.