Riyadh Bioremediation Facility

Challenge

Riyadh’s rapid growth from the 1970s onward dramatically diminished the hydrological regime of the Wadi Hanifah. By the 1980s, the water table had dropped below sustainable levels and desalinated water had to be piped in from the Eastern Province to meet increased consumption in the city. At the same time, the illegal dumping of solid and liquid industrial waste created a significant public health hazard, increased the risk of groundwater contamination, and contributed to the ecological degradation of the river corridor. The new urban wastewater bioremediation facility sought to provide a less costly alternative to a traditional mechanical plant while supplementing the hydrological regime of the wadi and reducing reliance on costly and environmentally-damaging treatment of salt water for recreational purposes.

Solution

While the bioremediation facility employs principles that have been applied before, both its size and the hybrid configuration of its natural and constructed features make it the first of its kind in the world. The facility’s design uses oxygenation to reduce concentrations of coliform bacteria colonies and biocells to create favorable habitat conditions for aquatic organisms and fish species that assimilate wastewater nutrients. It also employs complementary naturalized channels to provide continuous bioremediation of toxicants, harmful bacteria, and excess nutrients from urban and rural discharge during dry weather conditions. A monitoring program continually collects water samples at strategic locations, which helps determine the treatment efficiency of individual biocells, groups of cells, and the entire facility.

• The facility is primarily composed of 134 bioremediation cells organized into 3 main groups. These cells are responsible for the bulk of nutrient assimilation. The designed flow rate is approximately 84.8 cu ft per second with a retention time of approximately 31 hours. The biocells currently process an average of 92 million gallons of wastewater per day.
• Stone weirs at the inlet and outlet of each cell, along with pumps and aerating perforated pipes, provide sufficient levels of dissolved oxygen to support the removal of coliform bacteria and create favorable conditions for microbes, fish, and other aquatic organisms that absorb wastewater nutrients.
• Tilapia fish occupy the top of the food chain and control the growth of algae.
• The facility has its own wet laboratory for 24-hour monitoring.
• Educational programs are incorporated into the operation of the facility.

The bioremediation facility treats urban wastewater by augmenting the naturally-occurring process of nutrient assimilation into higher food chain levels. It incorporates physical components (pools, weirs, riffles, biocells, and an artificial periphyton benthic substrate), mechanical components (a submerged aeration system, 4 pumps, and a large jet fountain), and biological components (producers – algae, zooplankton, and higher plant life – and consumer organisms such as birds, fish and insects).

After collecting at the head pool of the facility, wastewater proceeds through 3 successive groups of 20, 34, and 80 biocells, and then collects into a 20-ft-deep aerating outlet pool before being released back into the wadi. Each biocell group is composed of an inlet channel, biocells, and outlet channels. The submerged aeration system in the inlet channel aggressively mixes the water to reduce blue-green algae propagation and provide the oxygen concentration levels required for the microscopic organisms responsible for consuming organic material and breaking down pathogenic bacteria. Wastewater enters the biocells at their head pool, proceeds through the central marsh channel and vegetated islands at the core of the cells, and meanders through a riffle zone before cascading through the cells’ outflow channel.

Each biocell’s head pool is lined with an artificial periphyton benthic substrate (in essence a synthetic algae-like surface) that provides plant and aquatic habitat and stimulates nutrient assimilation into the bacterial communities that sustain small fish. The central marsh channel, with islands of small shrubs and trees, provides additional aquatic and benthic habitat and supports larger plant species that in turn support larger predators such as herons and kingfishers. The riffle zone further oxygenates water and helps with the denitrification of bottom sediments.

• The rate of sedimentation throughout the facility proved faster than anticipated. This is in part due to improper maintenance during the first years of operation. To compensate, regular diving operations are required to remove accumulated sediment. In retrospect, the facility’s headpool should have been larger, though the area available for the project could have made this impractical. Design modifications are being investigated.
• The aeration pipes in the inlet channels are experiencing rapid calcification due to the hardness of the water and the pumping system employed. Proper dissolution of oxygen requires a thin veil or air bubbles pressure-generated through the pinholes in the pipes. Calcification clogs the pinholes and generates cracks or even failure. As a compensating measure, maintenance blow-out of the system has to be conducted every 2 months or so as opposed to the 6-month frequency originally recommended.

Project Team

Client: Arriyadh Development Authority, Saudi Arabia
Landscape and Planning Consultants: Moriyama & Teshima Planners Ltd., Canada
Engineering Consultant: Buro Happold, United Kingdom
Wastewater Consultant: Nelson Environmental Inc., Canada
Construction Firm: Badan Agricultural and Contracting Company, Saudi Arabia

Role of the Landscape Architect

The landscape architect served as main liaison with the client and coordinated all phases of the project. Responsibilities included facility design with other project consultants as well as contract documentation management, the supervision of implementation, and the development of operation and maintenance manuals.