Since 2008, tributyltin (TBT) has been banned due to ites adverse environmental effects. The current trend is to replace TBT with environmentally friendly coatings such as the tin-free self-polishing copolymer (SPC).

Other methods have evolved such as coatings with copper compounds and biocide boosters. Physical methods such as modification of surface topography, hydrophobic properties, and charge potential are alsobeing considered to prevent biofouling.

Hope this helps answer your question.

Professor Yehia Khalil

Yale University

USA

I had been working many years with reverse osmosis and other conventional systems for water treatment. There's no a biological (live microorganis) to help avoid the fouling. Organic chemical has been used but they are very dangerous(at the end they are biocides). A conventional alcaline-acid treatment is simple and less hard to the environment. The adjustment of the concentrations depend of your process (type of membranes basically).

Dear Gopi,

This text was taken from a review article contained in the link depicted at the end of this answer:

Among all the different solutions proposed throughout the history of navigation, tributyltin self-polishing copolymer paints (TBT-SPC paints) have been the most successful in combating biofouling on ships. The widespread use of these paints, estimated to cover 70% of the present world fleet in, has led to important economic benefits. Unfortunately, the TBT-SPC systems affect adversely the environment.

As an example, it has been shown that extremely low concentrations of tributyltin moiety (TBT) cause defective shell growth in the oyster Crassostrea gigas (20 ng/l) and imposex, development of male characteristics in female genitalia, in the dog-whelk Nucella sp. (1 ng/l). Malformations have been observed in many other species and the International Maritime Organization (IMO) also reports  accumulation in mammals and debilitation of the immunological defences in fishes. These facts forced the development of national regulations in countries all over the world:

• Restriction of the use of TBT-containing compounds on vessels less than 25 m in length.

• Restriction of the release rates of TBT-containing compounds from the paints.

• Elimination of the use of free TBT-holding compounds in paints.

Furthermore, after an International Convention held on 5 October 2001, parties to the convention are required to ban the application of TBT-based antifouling (A/F) paints from 1 January 2003, and the presence of such paints on the surface

of the vessel from 1 January 2008 (effective dates). Although the exact dates for the global application of the resolutions of the convention are still uncertain, regional legislations have already been developed in the same direction (e.g. Amendment to Marketing and Use Directive (76/769/EEC)).

Thus, the paint industry has been urged to develop TBT-free products able to replace the TBT-based ones but yield the same economic benefits and cause less harmful effects on the environment. The major antifouling paint companies (e.g.

International Marine Coatings, Hempel’s Marine Paints, Jotun, Ameron, Chugoku Marine Paints) have already decided to comply with the regulation by removing all TBT-based paints from their product assortment from 1 January 2003. The other party concerned, the shipping companies, has also started to react to the legislative changes by a fleet-wide conversion to tin-free paints (e.g. A.P. Møller and Leif Höegh)

In contrast to previous reviews, this paper seeks to combine all main topics related to antifouling (A/F) technology, and aims at a thorough picture of the state of art in marine biofouling prevention systems. Hence, it includes a description of sea water, an introduction to the biology of the fouling process, and a summary of the historical development of A/F paints. The latter covers not only biocide-based systems, by far the most used, but also alternative methods. This historical description leads to a discussion of tributyltin (TBT)-based systems and their tin-free biocide-based replacements, the analysis of which constitutes the backbone of the paper. Tin-free

biocide-based products are described by an analysis of their binder systems, pigments, and booster biocides used to complement the biocidal action of copper. In addition, the most promising options to dominate the A/F market in the future are presented and described.

Progress in Organic Coatings 50 (2004) 75–104

Review

Antifouling technology—past, present and future steps towards efficient and environmentally friendly antifouling coatings

Diego Meseguer Yebra, Søren Kiil∗, Kim Dam-Johansen

http://www.sailingteam.tuc.gr/TUC_Sailing_Team/INTERESTING/Entries/2014/2/6_MOURABIA_files/antifouling.pdf

Hoping this will be helpful,

Rafik

This is biofouling in membrane bioreactors - activated sludge systems - NOT biofouling on the surface of ships or marine structures.

Biological control of fouling in MBRs is still a research topic. The standard method is to live with it and aim to control it through scouring of the membrane surface, with periodic isolation of the membrane and treating with aggressive chemicals.

There have been studies on controlling through optimum selection of MLSS, DO, sludge age (related to MLSS), and the cycle settings on the scour of the membrane surface. I am not aware of any proven solution to date.

Dear Gopi

A phenomenon of fouling and especially biofouling is is a multi-faceted and a very complex phenomenon. Therefore this problem must be solved individually in each case, i.e. by the selection of appropriate membranes as well as process conditions. Membrane must be resistant to many factors i.e chemical, biological and physical conditions, to avoid all hazardous physical and chemical changes during long-term operation. Besides the choice of material (chemically resistant and hydrophobic), you should pay attention to the structure of the membrane. To prevent pores clogging of the membrane pores, they should be uniform and much smaller than the particulates of solids suspension. Regarding the operating conditions, safe selection of operating parameters (pressure temperature, flow rate) you should avoid concentration polarization, or provide for appropriate ways to reduce the concentration polarization.