Here is a start of topics, let me know if you need more...

■Carbon Abatement Technologies[CATs]

■Co-firing with a CO2-neutral biomass

■Supercritical and IGCC coal-fired power plant

■Saline aquifers

■Global Environmental Facility

■Environmental impact assessment and mitigation

■Water supply and treatment

■Wastewater conveyance and treatment

■Honey bucket systems

■Scrubbers

■Carbon capture technologies, CO2 transport, storage and use

■Global Practices of Environmental engineering law.

■underpinning technologies

■Electrostatic precipitators

■Catalytic converters

■Volatile organic compounds (VOC)

■Reactive organic gases (ROG)

■Recycled container housing

■Organic production of high-value products from seaweed

■Floating, ecological, multi-power source desalination plant

■Hyper-sound water-purifying system

■Green IT concept

■Treadmills that convert the rotation of the belt into electricity

■Designer shopping Cloth bags

■Reusing instead of recycling packaging

■Environmental policy and regulation development

■Contaminated land management and site remediation

■Hazardous waste management

■Solid waste management

Hi there,

First of all before choosing any topic i suggest you to look into some literature. Recent papers published in high ranked journals can give you a very good idea on where the world of research is going to. Then I suggest you to categorize the given areas and look for your interest. maybe you are interested in biological treatment of water. photo-catalytic reactions or membranes could be other topics. now a days looking for material with dual functions is getting a hot topic for example having non oxidants such as nano TiO2 in conjunction with another material such as alginate for example can give you and oxidizing agent plus an adsorbent. you can also make membranes from this composition as well and use it for your targeted pollution .

These are just some Ideas and the best way you can find a topic is by reading more on other people recent works. I really don't think you can get a topic for your Phd looking for it here. you might get ideas of course

Here is a start of topics, let me know if you need more...

■Carbon Abatement Technologies[CATs]

■Co-firing with a CO2-neutral biomass

■Supercritical and IGCC coal-fired power plant

■Saline aquifers

■Global Environmental Facility

■Environmental impact assessment and mitigation

■Water supply and treatment

■Wastewater conveyance and treatment

■Honey bucket systems

■Scrubbers

■Carbon capture technologies, CO2 transport, storage and use

■Global Practices of Environmental engineering law.

■underpinning technologies

■Electrostatic precipitators

■Catalytic converters

■Volatile organic compounds (VOC)

■Reactive organic gases (ROG)

■Recycled container housing

■Organic production of high-value products from seaweed

■Floating, ecological, multi-power source desalination plant

■Hyper-sound water-purifying system

■Green IT concept

■Treadmills that convert the rotation of the belt into electricity

■Designer shopping Cloth bags

■Reusing instead of recycling packaging

■Environmental policy and regulation development

■Contaminated land management and site remediation

■Hazardous waste management

■Solid waste management

As you can see from the other posts here, water treatment is a much bigger field than most people think. We've got phsyical treatments (filtration and flocculation), chemical treatments (softeners and bleach/UV/ozone disinfections), biological treatments (mostly active-sludge based techniques to remove organic matter and nutrients from wastewater), ecological treatments (wetlands as filtration and sequestration media), flow and distribution engineering, waste management for those techniques that involve sludge or brine, treatment plant site selection and design, different grades of purification: drinking water, recreational water, industrial water, etc. and even hydro-electric power generation. So it really depends on which particular aspect interests you more than the others. If you're more into architecture and urban planning, try something with the city to upgrade their treatment plant or distribution system. If you're more into the chemistry, evaluate the efficiency of UV photolysis or some advanced oxidation techniques on removing some contaminants. If you're into microbiology, look at optimization of activated sludge for nutrient removal to control algae blooms. If you're into macrobiology, look at the efficiency of different types of wetland plants at retaining contaminants from the water. If you're really more of a process/chemical engineer, look at ways to improve on desalination techniques by changing the membranes or something like that.