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Case Study 8:Wastewater Treatment Using Water Hyacinth in Iraq

The use of the water hyacinth plant for wastewater treatment is considered a simple technology that does not require costly machines or equipments, a large labor force, or complex maintenance processes. It requires only large areas of land and a hot climate. In view of the renewed interest on utilization of unconventional water resources, including wastewater, and the desire for reduced environmental contamination at surface water sources, the possibility of applying this technology is being studied. Its application is particularly important in scattered rural areas with small residential communities, to prevent the spread of disease, and to help preserve the natural beauty of villages and rural areas.

Technology Description

Water hyacinth (Eichhornia Crassipes (Marri) Solms) is a hybrid plant from the Pontederiaceae family. It exists in the equatorial and semi-equatorial areas in the world, and wastewater is considered a suitable environment for the growth of the plant. When it is planted in a wastewater pond, it grows vigorously, with roots extending to depths between 10-30 cm below the water surface (Figure 69), while its stem and leaves rise to the water surface and sometimes cover it completely. The plant can obtain its nutrients (phosphorus, nitrogen) from the wastewater. The fine roots of the plant trap suspended solids, and present a suitable environment for the growth of microscopic organisms that feed off the organic materials present in the wastewater, transforming them into simple inorganic material. The result is the production of clean water with low concentrations of BOD, suspended sediments, phosphorus and nitrogen. The cleaned water can be released directly into rivers, or used for drinking or domestic purposes after carrying out other additional processes (e.g., disinfection).

Figure 69. Descriptive sketch of the water hyacinth plant

This technology was first applied experimentally in September 1994 as a research project in Iraq in the area nearby Al-Rostomeyah plant, with the goal of investigating its suitability for the climatic conditions of Iraq.

The study included two phases of field experiments. The first phase was conducted during winter, using a stagnant water system. The experiments were conducted for different types of water, using several concrete tanks in the Wathbah plant in Baghdad, to identify the most suitable type of water for the growth of the plants. The second phase was carried out during summer in Al-Rostomeyah plant, using a continuous water flow system. Small ponds were used to study the effect of plant growth stages, the changes in the organic loads, the duration of water treatment, and the effects plant harvesting (reducing their density) on the treatment efficiency. One pond was used as an observation pond for monitoring purposes.

Stagnant Water System

Four identical concrete ponds were constructed (surface area of 1x1 m and depth of 0.8 m) in Al-Wathbah plant to investigate the ability of the water hyacinth plants to grow under stagnant water system conditions. The objective also was to investigate the type of water most suitable for plant growth. The tanks were lined with two layers of nylon to prevent water leakage (Figure 70), as well as an additional nylon layer to be used as a cover in case of cold or rainy weather.

Figure 70. Schematic diagram of basins in stagnant water system

The study was conducted on four different types of water, through two identical tanks for each type of water. For all types of water, one of the two identical types was used for comparison purposes (reference), while two water hyacinth plants were planted (wet weight of 150 gm) in the second. The water level inside the tank was kept constant (0.35 m) throughout the duration of the experiment, with the water lost through transpiration or evaporation being replaced. The types of water used in the experiments included (1) primary-treated wastewater, (2) secondary-treated wastewater, (3) saline water taken from a drain, and (4) raw water taken from the Deggla River After 3 weeks, the plants started to grow and spread on the water surface, although at different rates between tanks, based on the quality of the water in the tank. The tank containing primary treated water produced the best plant growth, with no growth of algae being observed. After 4 weeks, the plants completely covered the surface of the tank. Less plant growth occurred in the tank containing the secondary-treated wastewater, and some algal growth was observed. The raw water produced slow and little plant growth, while the saline water produced practically no plant growth.

The sampling process continued from 1 April to 1 August, 1994. Samples were taken weekly at a depth of 0.15 m and analyzed for biochemical oxygen demand (BOD), ammonia-nitrogen, nitrate-nitrogen, nitrite-nitrogen, phosphate, sulfate, sodium, potassium, calcium, magnesium, pH, electrical conductivity and alkalinity. At the end of the experiment, the plants were taken from the tanks and dried, and the total nitrogen, phosphorus, organic material, sodium, and potassium content determined.

Continuous Flow System

Two rectangular ponds were prepared (area of 2x1 m, and depth of 0.8 m), with a trapezoidal cross section, in the area nearby Al-Rostomeyah Plant (Figure 71).

Figure 71. Schematic diagram of continuous flow pond

The two ponds were covered with a nylon cover, with a sand layer to prevent water leakage. The pond was provided with water through a 2-6 cm diameter pipe that extended to a depth of 0.15 m inside the pond. The other end of the pipe was connected to a 200-liter capacity reservoir containing primary-treated water. Another pipe of the same diameter was provided to withdraw the water from the pond.

The two ponds were filled with the same water. Four water hyacinth were planted (wet weight of 170gm each) in one pond, while the other pond served as a reference (Figure 72).

As shown in Table 46, several variables were studied in this phase of the study, including the release rate, water depth, duration of water residency, and the effect of these variables on plant growth.

 

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