Wastewater Reclamation by Reverse Osmosis —
Treatment of Wastes Produced
SOTIRIOS G. GRIGOROPOULOS, Professor
J. CHARLES JENNETT, Assistant Professor
Civil Engineering Department
University of Missouri—Rolla
Rolla, Missouri
INTRODUCTION
The growing population and expanding industrialization of the country
continually require more and higher quality water. To meet this demand, new
sources of water need to be developed and the quality of all waters must be
protected. Reclaimed wastewater constitutes a major, yet untapped, source of high
quality fresh water, and the development and application of methods for wastewater
reclamation must be accelerated (1).
Reverse osmosis offers considerable potential as a means of reclaiming
municipal wastewater. The process consists of driving the water under pressure
through a semipermeable membrane; the membrane blocks the passage of the
inorganic and organic impurities, while allowing virtually pure water to flow through.
Originally developed for the desalination of ocean and inland saline waters, reverse
osmosis has been employed to reclaim municipal waste treatment plant effluents (2).
Alternately, this method may be used to renovate raw sewage (3); however,
pretreatment by chemical coagulation and sedimentation will be required to remove
solids which would otherwise have mechanically blocked the membrane.
Unfortunately, the reverse osmosis process also produces wastes (Figure 1).
These include the raffinate, or the concentrated wastewater which cannot be totally
reclaimed, and the sludge which results from the chemical pretreatment. The
raffinate contains in concentrated form all the dissolved organic and inorganic and
some of the colloidal materials originally present in the sewage; while the sludge
contains colloidal and suspended organic materials along with the precipitated
coagulants such as hydroxides of aluminum of iron. These wastes, which have a
rather unique character, must be effectively treated before they are released to the
receiving waters.
This paper reports on the treatment of the wastes produced by a reverse
osmosis plant reclaiming municipal wastewater, and presents studies undertaken to
evaluate the treatability of the raffinate and the raffinate-sludge combination in
activated sludge systems, and of the metal-containing primary and secondary sludges
in anaerobic digestion systems.
336