Keywords: Wastewater treatment, membrane technology, irrigation.
Secondary or less treated effluent is used for irrigation in the entire Jordanian — Palestinian — Israeli region. Its use poses environmental and health risks and raises soil salinity and alkalinity.
Advanced tertiary treatment membrane technologies, based on ultra filtration (UF) and reverse osmosis (RO), yielding effluent of suitable quality for unrestricted irrigation were introduced and researched.
Effluent analyses showed that the UF membrane removes most of the pathogens and organic matter present in the secondary-treated effluent, and the RO membrane removes dissolved solids.
UF membrane performance decreases with time due to fouling, caused by adsorption of suspended or dissolved substances inside membrane pores and on surfaces. Cleaning procedures, such as backwash and chemical flushing must be done.
Field and greenhouse irrigation experiments testing a) effluents from secondary treatment containing relatively high concentrations of organic matter, plant nutrients and salts; b) UF permeate, still containing salts; and c) mixtures of UF and RO permeates, low in salt content.
Soil salinity measurements indicated that the use of secondary treatment effluent raises soil salinity considerably in comparison to the membrane treated ones. Measurements of water emission rates from drippers showed the capability of UF and RO treatments to minimise clogging.
In one site several consecutive crops were grown over six years in plots receiving irrigation water from the same effluent treatments. With time, cumulative effects of irrigation water quality became significant. Yield measurements showed a significant negative correlation between yield obtained and increased soil salinity, induced by irrigation water quality, resulting from effluent treatment.
In lysimeter experiments with ryegrass in a clay soil, irrigation with secondary-treated effluent for about 10 years raised its salinity by approximately 50% compared to irrigation with fresh water. Also accumulation of organic nitrogen and doubled concentration of labile phosphorus fractions were found.
Upon seeing the advantages given by membrane treatment of secondary treated effluent, membrane plants operating on a relatively large scale were constructed to serve as a model for practical application in the entire region.
In parallel, it was found that the activated sludge process reduces total microbial count to about 10% of the initial count and to about 1% when chlorination is applied.
J. Hagin, Grand Water Research Institute, Technion – Israel Institute of Technology, Haifa, Israel. (Corresponding author).
M. Khamis, A. Manassra, J. Abbadi and M. Qurie, Al Quds University, East Jerusalem, Palestinian Authority.
A. Bulad and L. Al Hadidi, National Center for Agricultural Research and Extension, Amman, Jordan.
R. Semiat, A. Shaviv, I. Katz and C. Dosoretz, Grand Water Research Institute, Technion – Israel Institute of Technology, Haifa, Israel.
O. Blonder, Peres Center for Peace, Tel Aviv – Jaffo, Israel.
23 pages, 22 tables, 15 references.