Effects of Wastewater Reuse on Soil Condition: A Study on Organic Matter Enrichment

1. Wastewater Reuse for Irrigation : an Acceptable Soil Conditioner?Nicholas KathijotesDepartment of Civil EngineeringHigher Technical InstituteNicosia-Cyprusnkathijotes@hti.ac.cy

2. Abstract • Drought climatic conditions occurring around the Mediterranean region and the Balkans, suggest serious consideration as to the reuse of treated effluents resulting from treatment of domestic effluents. Taking into account that about 70% of the total water resources are used for agricultural purposes and mainly irrigation, then a tremendous conservation of hydrological resources can occur. Using however non-conventional quality water for irrigation, presents a number of ecological and health risks and poses problems connected with soil and ground water contamination. This paper concentrates in the general evaluation of the effects of these effluents on soils, and investigates and evaluates their effects in terms of organic matter enrichment and soil conditioning

4. TREATEDSEWAGE. Electrical Conductivity in dSm-1 and soluble cations-anions of water meq/l.

5. CHARACTERISTICS OF GROUND FARM-WATER USED • The following were the major characteristics of the ground water used: • high content of soluble elements toxic to agriculture • electric conductivity = 3.0 mmho/cm • from the cations predominant is Na+ = 21.7 mg/l • from the anions predominant is Cl = 15.5 mg/l • It should be noted that Na2CO3 is one of most toxic to crops

6. Soil profile evaluation, (SAR).

7. SALTS EVALUATION • A typical example in the presentation of the results as shown in the previous slide, SAR (sodium absorption ratio) is investigated by the application of various salts evaluation criteria at each increment of the soil profile under investigation. One may notice that the quality of the samples irrigated with groundwater obtained from nearby wells demonstrates higher values of SAR and therefore poses greater salinisation risk. This is due to the fact that most ground waters in Cyprus, due to their high content of calcium carbonate in the soils , present high level of salts. • Soils of electrical conductivity below 4 dS/m and high values of SAR, between 13 and 15,are considered as sodic soils. These soils also demonstrate high pH values, usually above 10, and present various agricultural problems ,which are however manageable if proper care is given. Next slide shows the pH evaluation of our profile.

8. pH Evaluationof Soil Profile

9. Organic Content Evaluation on Profile

10. CONCLUSIONS • It is clear that ingredients contained in treated wastewater may create undesirable effects on soils and groundwater. However, careful management may overcome these effects. Soils in Cyprus are generally of low organic content. It is evident that by using treated wastewater for irrigation, besides the great savings in hydrological resources, the organic content of soils increases by about an average value of 21% of the soil profile. Due to this increase of organic matter; soils demonstrate structural improvement and consequently improvement of soil fertility. Structural improvement improves soils mechanically, and as a result the resistance to erosion is increased. This may be of greater interest in the restoration of disturbed land. Most of the humus that originates from treated sewage irrigation is gathered at the first 60cm of the profile and consequently around the plant root zone, which is highly beneficial to plants. • It is however suggested that all factors should be well considered before planning a wastewater reuse network.

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