An aerial view of the Kassler slow-rate sand filtration plant shows the six basins with one basin emptied for scraping. This plant has served the Denver Water Department for more than 80 years.A survey of 27 slow sand filtration plants in the United States indicated that most of these plants are currently serving communities of fewer than 10 000 persons, are more than 50 years old, and are effective and inexpensive to operate. A slow sand filtration research facility in Logan, Utah, was compared with the operating plants to determine if locally available, unsieved sand achieved similar results. The 75ms/d research facility performed well in removing turbidity, coliform bacteria, and particles of a size representative of Giardia cysts.

Organic silicon polymers (siloxanes) are increasing in use and are increasingly being detected at municipal sewage treatment facilities and landfills. Several forms of siloxanes are volatile and have been detected in gas evolved from the anaerobic digestion process at many publicly owned wastewater treatment plants (WWTPs). The presence of siloxane compounds in digester gas used to fuel internal combustion engines that generate electricity and heat power (cogeneration) causes severe engine maintenance problems that are related to silicon deposits in piston cylinder and valve head assemblies. At the Annacis Island WWTP in Vancouver, British Columbia and at the Alvarado WWTP in Union City, CA, siloxane related engine maintenance problems lead to decisions to terminate digester gas fueled engine operations.Both plants were motivated to quickly identify and implement systems to mitigate siloxane related engine maintenance problems. After quick review of available options, both plants implemented digester gas treatment systems consisting of gas dehumidification followed by activated carbon adsorption. Activated carbon systems were simple and relied on replacement of exhausted carbon as opposed to on-site regeneration. Activated carbon was extremely effective at eliminating siloxanes from digester gas and carbon life was as expected or better. Removal of siloxane resulted in reduction of build up of silicon in engine oil and dramatic improvements in engine operation as well as reduction in maintenance costs. Maintenance cost reductions greatly exceeded the cost of operating the siloxane removal system.

A new Trickling Filter / Solids Contact (TF/SC) process was designed, constructed, and commissioned for the City of Hayward, CA in the 2000 -2010 decade. Modern design features were employed for system components that provide flexible and energy efficient process control. The design included further development of a TF biofilm predator control system that provides operators with opportunities to inhibit proliferation of snails and other nuisance organisms in the TF system. Commissioning experience provided a notable confirmation of the effect of TF organic loading on the bioflocculation performance of the coupled solids contact process.

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