75    COMBINED TREATMENT BY AERATED PONDS AND
CHEMICAL CLARIFICATION COMPLETED BY
RECIRCULATED COOLING SYSTEM
N. Galil, Senior Lecturer
M. Rebhun, Professor
Environmental and Water Resources Engineering
Technion — Israel Institute of Technology
Haifa, Israel
Biotreatment of wastewater from an integrated oil refinery by activated sludge and by RBC was
studied and reported by the authors in previous Purdue Industrial Waste Conferences. The objective
of this study is to develop a low cost process combination by utilizing facilities, which exist in most
industries, as treatment means as well as recipient for the renovated effluent. The idea is to share the
task of the bioprocess between: a) a partial primary stage biotreatment by two aeration ponds (AP); b)
chemical clarification of the primary stage effluent for removal of MLSS and colloids synthesized in
the first process, by utilizing the existing lime clarification-softening system; c) completion of the
bioprocess by a recirculated cooling system (RCS) which has a high biooxidation capacity and also
reuses the clarified effluent as make-up. The paper analyzes experimental data obtained from a pilot
plant including two aerated tanks in series with a total hydraulic residence time of 2 days, followed by
a lime clarifier. The main characteristics of the AP process is that hydraulic and sludge residence times
are identical; two days are considered as very short SRT, especially in petrochemical wastewater, while
in activated sludge SRT is usually above 15 days. The AP removed 60% of the COD—15% by
stripping —and 80% of the BOD; the oil removal was up to 50%. The chemical lime clarification
improved the AP effluent reducing: suspended solids from 160 to 8 mg/1; oil from 34 to 9 mg/1; total
COD from 290 to 170 mg/1. The study includes data on volumes and characteristics of the chemical
sludge produced. The organic matter residual from previous treatment stages, most of it in soluble
form, will be biodegraded in the RCS. The characteristics of RCS working as biological reactor were
studied by Rebhun et al. and reported elsewhere. This study emphasizes economy in capital investment and beneficial reuse of industrial wastewater. The combined system includes two biological
barriers, AP and RCS, combined with the chemical clarification barrier, providing reliable and a low
cost process combination.
INTRODUCTION
Refinery wastewater biological treatment data has been reported for many years. The data demonstrates efficient stabilization in the activated sludge process in which the biota metabolize the refractory components after long acclimation periods'. Adding adapted mutant bacteria has been suggested
by others2,3. The presence of parafinic and aromatic hydrocarbons affects biofloc settling adversely
and their biodegradability rate is much lower than that of municipal type organic material4.
Phenols are a major component of refinery wastewaters, being produced in the cracking process
and special gasoline washeries. While many report that phenol is a controlling toxicant in biological
treatment5,6, others report efficient phenol removal at influent concentrations up to 200 mg/1, after
acclimation, which requires, however, a long reactor residence time to achieve good biofloc
settleability7.
The wastewater of the integrated refinery reported in this study is pretreated by gravity oil-water
separation, followed by flocculation and dissolved air flotation. The effluent contains 60 to 280 mg/1
BOD, 260 to 710 mg/1 COD, 20 to 170 mg/1 hydrocarbons; the phenols concentration was 2 to 6 mg/1,
after taking concentrated phenolic streams, accumulated in the refinery, to separate treatment.
The severe regional water shortage, imposed to reuse treated effluent as make up in the cooling
water system, minimized effluent discharge to the river. Biological treatments by activated sludge or
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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