Effective Phosphorus Removal
by the Addition of Alum
to the Activated Sludge Process
DAVID R. ZENZ, Research Chemist III
Research and Development Group
JOSEPH R. PIVNICKA, Civil Engineer IV
Maintenance and Operation Department
The Metropolitan Sanitary District of Greater Chicago
Chicago, Illinois
INTRODUCTION
There has been increasing concern over effective means of abating excessive
nutrient enrichment of receiving waters which then develop prolific growths of algae.
These algae growths '.iave an impact upon the aesthetic and economic use of a surface
water. Algae discolor water and when they die off and decompose, release malodors
to the water and the atmosphere. Clogging of filters with algae increases water treatment costs and causes problems in water purification.
Sanitary engineers have long realized that domestic and industrial wastewaters
are a rich source of the critical nutrients which cause algae to flourish. Recently,
interest in arriving at a wastewater treatment method to remove offending nutrient
elements before effluent discharge has been renewed.
Sawyer (1) established that the removal of phosphorus is an effective and
feasible way of retarding algae blooms in most surface waters. Since conventional
wastewater purification does not ordinarUy produce low effluent phosphorus concentrations (2, 3, 4), supplemental removal methods have been widely investigated.
Based upon economic and performance evaluations (2) chemical removal
techniques hold the greatest promise for general application. To date, many methods
(5, 6, 7, 8) have been investigated but few have combined chemical and biological
treatment.
The use of metallic flocculants for simultaneous flocculation of the biological
masses and phosphorus removal has been investigated with success by Tenny and
Stumm (9, 10). The activated sludge system has essentially two separate operations:
1) Adsorption of suspended material and soluble substrate uptake, and 2) Flocculation
of the biological particles. Adding metallic precipitants to the activated sludge process not only wUl remove phosphorus but should aid the flocculation of the biological
masses.
This combination of chemical and biological treatment has been tried by
Thomas (11, 12) who used principally ferric and ferrous salts as precipitants. He has
reported phosphorus removals as high as 92.4 per cent with 10 mg/1 of Fe3+.
Barth and Ettinger (13) added 10 mg/1 of Al3+ as sodium aluminate to a
activated sludge pilot plant and reported phosphorus removals above 90 per cent.
Object of this Investigation
It was the object of this research to evaluate under actual plant conditons a
combined chemical-biological process capable of producing a wastewater low in effluent phosphorus BOD and SS.
-273-