Wastewater Treatment

Constructed Wetland for Wastewater Treatment
Conventional wastewater treatment plants involve large capital investments and operating costs. In developing countries most of these systems fail because of high energy and maintenance costs. Constructed wetlands are low-cost alternative for treatment of wastewater especially for those areas where land availability is not a problem. They are simple to build, easy to maintain and operate, and have relatively low energy requirements.
A pilot-scale constructed wetland (CW) has been built at NED University. Treatment performance of this CW is being evaluated for various physical, chemical and microbiological parameters under local climatic conditions.


Figure: Constructed Wetland at NED University
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Treatment of Refinery Wastewater using Vertical Flow Constructed Wetlands
Pilot scale constructed wetlands were used to treat refinery wastewater. The experimental set up consisted of four vertical flow constructed wetlands (CW) with different plants and media. CW 1 was planted with common reed (Phragmites), CW 2 was planted with phragmites plus additional layer of sludge over the media, CW 3 was planted with cattail (Typha) plus additional layer of sludge over the media while CW 4 was planted with Typha. Experiment was conducted at Karachi (Pakistan) with a warm humid summer (38ºC) and a normal cold winter (10ºC). After acclimatization period, wastewater from a local refinery was added manually to maintain a hydraulic loading rate of 85 mm/d. The four CW removed all monitored pollutants with good removal efficiencies during the initial monitoring period: turbidity (91%, 72%, 96%, 95%); suspended solids (87%, 86%, 86%, 73%), oil and grease (77%, 80%, 60%, 83%), COD (57%; 47%; 53%, 72%); BOD (37%, 49%, 33%, 36%); sulphate (62%, 77%, 85%, 76%), chloride (96%, 95%, 98%, 98%) and total phenol (68%, 98%, 98%, 97%). Overall CW 4 showed the best performance in removing pollutants. For phenol removal, CW 2 and CW 3 performed better than CW 1 and CW 4. With regard to type of plant species, wetlands with Typha performed better than those planted with Phragmites.


Figure: Vertical Flow Constructed Wetlands to Treat Refinery Wastewater

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Treatment of Produced Water from a Gas Field using Free Water Surface Wetland System

A pilot scale free water surface (FWS) wetland system was built at a gas field in Sindh province of Pakistan. The pilot system consisted of two treatment cells, cell 1 was planted with Phragmites while cell 2 with Typha. Initial monitoring of the wetlands for removal of hydrocarbons started in July 2013. The average influent BTEX values were as follows: benzene (0.9 mg/L), toulene (0.1 mg/L), ethyl benzene (0.2 mg/L), m-xylene (1 mg/L) and o-xylene (0.1 mg/L).The FWS wetland system removed all monitored contaminants with good removal efficiencies during the 6 months monitoring period: benzene (89.1%), toulene (89%), ethyl benzene (97%), m-xylene (88.1%) and o-xylene (80.2%).


Figure: Free Water Surface Wetland System in a Gas Field to Treat Produced Water

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Floating Constructed Wetland for Improving Wastewater Treatment Efficiency of a Pond System
Floating Constructed Wetland (FCW) is an innovative variant of constructed wetland technology in which stems of the plants remain above the water surface while their roots extend into the water column beneath the floating mats. A pond system treating wastewater at NED University campus was retrofitted with a FCW. The floating wetland was made using PE insulation sheets. Three different plant species were planted; Typha, Canna (Red, Green, Yellow and Green) and Cypreus Papyrus. The FCW improved TSS removal by 34 %, DO was also increased from 4.5 mg/L to 5.5 mg/L, indicating a 35% increase with introduction of FCW. The FCW also successfully stabilized organic matter. CW further improved the removal efficiency in the range of 26% - 46%. They also improved the nutrient removal efficiency and pathogen removal.


Figure: Established plants in FCW placed in a Pond system

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