Sanaa Sewage: Health & Environmental Risks [Archives:1998/01/Health]
* By Sadek Al-Osaimi
Evaluating the Quantity and Quality of Sanaa Sewage is a research done by Eng. Faysal Ahmed Nasser for which he got an M.Sc degree with distinction from Sanaa University. Supervised by Dr. Abdullah Ba-Baqi, the research concentrated on the use of sewage water for irrigation purposes. People living in and around Sanaa suffer from several environmental problems emanating from the bad sewage management, which has aroused much controversy within society. Research done in this field has uncovered many environmental facts hitherto unknown to the general public. Eng. Faysal Ahmed Nasser spent two years to study the quantity and quality of sewage used for irrigating small farms in the Sanaa vicinity. Usually, sewage from Sanaa is first collected in treatment basins in the Al-Rawdha area, and is later sent to the farms in Wadi Hawat. However, some of the sewage is sometimes sent immediately to Wadi Hawat, without proper treatment. Crops irrigated by sewage include corn, wheat, onions, and barley and clover which are used as animal feed. The overall daily sewage flux going into Al-Rawdha sewage works in around 14,000-39,000 cub.m i.e. 23-64% of the Sanaa sewage. The rest – 37-77% goes directly to irrigate farms. Relying on accurate chemical, physical, and microbiological analyses, Eng. Nasser’s study uncovered several health and environmental problems related to inadequate sewage management and disposal. Fecal colon bacteria is found to be quite endemic in agricultural fields irrigated by sewage (17×106 cultures per 100 ml). Also, ten days after each irrigation process, 35 cultures of bacteria remain alive on every 50g of onions. Ammonium nitrate concentration was found to be 100mg per liter – quite harmful for nitrate-sensitive plants. Suspended solids in the sewage (352mg per liter) can lead to plugging the soil’s pores thereby preventing air and water from permeating through. These organic materials then decompose in an airless environment causing foul odors. Moreover, water wells 10-40 m deep that lie on the sewage route become completely contaminated. The extent of contamination decreases in deeper wells – 100-400m. The study, however, did not clarify any likely changes to the soil’s characteristics. But the plant nutrient concentrations of nitrogen, phosphorus, and potassium were estimated to be 8, 0.5, and 2 tons for every hectare of land respectively. Other important figures found by the study include the following: * Concentration of organic matter: BOD = 324 mg per liter; COD = 1,100 mg per liter. * Electrical conductivity = 2268 microsiemen/cm. * Dissolved salts = 1725 mg per liter. * Sodium, Fluoride, & Boron = 207, 250, & 1mg per liter, respectively. * Heavy elements: Cadmium, Chromium, Copper, Iron, & Lead = 0.25, 0.20, 0.13, & 0.18 mg per liter, respectively (acceptable levels).
The study concluded with a number of recommendations to improve the overall sewage management: – Sanaa sewage must be treated to an acceptable level for farm irrigation; – more studies should be conducted to ascertain the extent of health hazards caused by partial sewage treatment, especially among people living on or in the vicinity of farms irrigated with sewage water; – the extent of sewage pollution of the underground aquifers must be further studied; – changes in soil characteristics must be followed over a long period of time; and there are several other pertinent recommendations.
* Sadek Al-Osaimi, Environment Protection Council Mr. Al-Osaimi also wrote the article entitled Yemen Turtles & Tortoises on the last page of issue 51 of the Yemen Times. His name was omitted due to a technical error.