Reflections on Seven Decades of AS History
Reflections on Seven Decades of AS History
(Water Pollution Control Federation, 1985)Authors: James E. Alleman and T.B.S. Prakasam |
I. INTRODUCTION
Although educated extensively in the technical details of activated sludge treatment, relatively few contemporary environmental engineers are aware of its colorful historical development. On the one hand, it might be argued that a knowledge of activated sludge history is superfluous to the task of its practical application. And yet, for a process in which billons of dollars are currently invested, professional curiosity alone should foster an interest in the origins and geneology of activated sludge.
Generally regarded as the conventional norm for wastewater treatment, the activated sludge process has certainly drawn substantial engineering interest over the past seven decades. Just three years after the phrase and concept was originally coined in 1914, Porter\ul\d compiled a remarkable bibliography of 200 references dealing with activated sludge. And with his second edition in 1920, the number had grown to 800\u2\d.
Subsequent authors (i.e. Ardern, 1917\u3\d; Martin, 1927\d\u4\d; Clark, 1930\u5\d; Mohlman, 1938\d\u6\d; and Greeley, 1945\d\u7\d) have, in succession, provided informative chronological reviews covering the ever-expanding history of activated sludge treatment. The last in this series was Sawyer's classic 1965 article on activated sludge milestones.\u8\d
In this context, the paper at hand will unavoidably retrace technical developments documented by preceeding activated sludge historians. As a different slant on the topic, though, emphasis will be placed on extracting the personal and/or professional interest items which embellish and enrich the historical evolution of activated sludge treatment.
In order to understand the impact which activated sludge had on wastewater treatment technology, one must first appreciate the relative infancy of the field which existed during the late 1800's and early 1900's. Biological treatment was unquestionably a primitive science in this era, having only recently been elucidated through progressive European (i.e. Mueller, Frankland, Bailey-Denton, Dibdin) and American (i.e. Mills, Hazen, Drown and Sedgwick of the Lawrence Experimental Station, Massachusetts) filtration research.\u9\d The basic derivatives of their work included intermittent filters, contact beds and trickling filters. Septic tanks were also popular during this era. However, Cameron obtained a restrictive patent in 1896 and began to enforce substantial royalty charges despite bitter public criticism.\ul0\d Although the popularity of septic tanks subsequently faded, alternative anaerobic systems were soon available, including both the classic Imhoff Tank and its predecessor, the Travis `Colloider' or `Hydrolytic' Tank.\u9\d Imhoff also patented his unit, but the associated royalty charges were considerably lower.\u11\d
Physical-chemical systems were perhaps somewhat more popular, including basic dilution, sedimentation, chemical treatment, and electrolytic treatment (i.e. the so-called direct oxidation process).\u9,12\d Overall, though, none of the available wastewater treatment technologies produced a top quality effluent. With most of these systems encompassing anaerobic conditions in some fashion, aesthetic factors alone fostered widespread dissatisfaction. In this context, municipalities were, therefore, ripe for the announcement that activated sludge could produce an exceedingly clear, non-odorous effluent.\u13\d
III. PRELIMINARY `BLOWING-AIR' RESEARCH
Searching for an improvement in sewage treatment, and with an intuitive inclination that aerobic conditions would avoid undesirable, malodorous anaerobic results, several researchers began to explore blowing air into sewage tanks. Dr. Angus Smith's work in 1882 is commonly referenced as the original study, followed by Dibdin and Dupre', Hartland and Kaye-Parry, Drown, and Mason and Hine.\u4,14\d For the most part, these early pioneers felt that oxygen presence `per se' would provide the desired oxidation of wastewater contaminants. Experimental results, though, were nominal at best. Although putrescence was typically delayed, the effort and expense of aeration seemed to lack significant compensation in terms of improved treatment.
Somewhat greater success was obtained, however, in studies of artificially aerated filters conducted by Waring, Lowcock, and at the Lawrence Experimental Station.\u4,9,14\d In hindsight, it is evident that these latter fixed-film units were receptive to the stimulus of aeration because of their existing biomass, whereas the earlier aeration tanks lacked a recycled biological population.
Over the course of the next few years, the importance of a suspended precipitant for enhanced biological treatment became more accepted. Studies conducted by Mather and Platt in 1893 revealed that precipitated impurities which accumulated at the bottom of aeration tanks provided a marked enhancement of available treatment.\u4\d In his presentation to the Royal Commission in 1905, Adeney reinforced this belief that collected humus matters would accelerate the treatment capacity.\u4,14\d Fowler's experiments on sewage aeration in 1897 also yielded a clear effluent with rapid settling deposits of particulate matter.\u4\d However, Fowler conversely viewed the enhanced deposition as a failure since he personally believed that sewage impurities were to be rendered soluble or gasified for optimal treatment.
By 1910, the merits of aerating sewage in the presence of biological humus or slime were beginning to find widespread acknowledgement. In their classic full-scale New York study, Black and Phelps decided to abandon coarse rock media in favor of closely spaced, wooden laths in order to achieve a higher surface area for desired slime accumulation.\u15\d In essence, their unit was an aerated version of the prior Travis `Colloider' or `Hydrolytic' Tank (which had also used wood laths, but in an anaerobic contact chamber).\u9,16\d
Clark and Gage also initiated similar laboratory studies at Lawrence in 1912, comparing aerated treatment efficiencies of bottles inoculated with algal suspensions against that obtained in packed slate beds.\u4,14\d The slate bed concept should, however, be attributed to Dibdin.\u17\d Having been unsuccessful at simple aeration in 1884, Dibdin had successively studied intermittent filtration, contact beds and serial contact beds before coming full circle to the notion of combining aeration with biological treatment in a slate bed contactor.
IV. `BOMBSHELL' DISCOVERY
Given these concurrent studies at New York and Lawrence, it was, therefore, serendipitous that the emminent Englishman, Gilbert John Fowler, was called to the United States to review the New York Harbor pollution problem.\u4,14,16\d In conjuncton with this trip, Fowler had an opportunity to witness first-hand the Lawrence experiments in 1912. Fowler subsequently credited this visit as the impetus for his "illuminating idea" regarding activated sludge, referring to Lawrence as the "Mecca of sewage purification." \u18\d
Although disappointed with his prior aeration experiments, Fowler quickly seized upon the concept of employing a suspended biomass culture and initiated several related experiments upon returning to Manchester, England. One year after the Lawrence tour, Fowler and Mumford published their successful results covering a suspended-culture aeration system inoculated with iron salts and a select M-7 bacterial seed.\u19\d Their treatment scheme sequentially employed a `blowing tank' and clarifier, but a lack of solids recycle necessitated continuous inoculation with the M-7 organisms.
At this point, 3l years had elapsed since Dr. Smith first examined the aeration of sewage. However, the seemingly simplistic notion of accumulating a suspended biomass through solids recycle was still unknown. Hence, the revelation by Fowler's students, Ardern and Lockett, in May 1914 that these humus solids should be saved rather than discarded proved to be an unqualified "bombshell" (Fowler's description, provided during an audience reply following presentation of this paper).\u18\d Ever sensitive to the fiscal realities of academic research, Ardern and Lockett gratefully acknowledged monetary support provided by the Worshipful Company of Grocers.\u20\d
Using fill-and-draw cycling, these latter authors had provided the premier demonstration and pronouncement of activated sludge treatment. Even when viewed in the context of our contemporary operations, their initial experiments were remarkably advanced. Indeed, their presentation addressed such topics such as energy conservation, sludge handling, and the sensitivity of nitrifying organisms to temperature and pH, all of which are still debated in our contemporary literature. Perhaps more importantly, the audience for Ardern and Lockett's presentation immediately recognized the monumental value of their discovery.
V. PRAGMATIC ADVANCEMENT
Ardern and Lockett subsequently presented two further papers in 1914 and 1915 which provided additional information on the following topics: performance capabilities during continuous-flow and fill-and-draw operation, the detrimental impact of trade wastes, aeration levels using plain tubes and porous tiles, required aeration intensities and biomass acclimation.\u20,21\d Even as their pioneer research continued, though, the process was being tested on a full-scale basis. In fact, at the same 1914 meeting that Ardern and Lockett presented their second paper, Melling\u22\d announced that he had successfully applied activated sludge treatment to an 80,000 gallon per day flow at Salford, England.
In quick succession, several full-scale English installations were placed into operation. The following listing provides a chronological summary of these facilities:\u4,10,14\d
1914 - Salford, England - 80,000 gpd at fill-and-draw operation
- 12,000 gpd at continuous-flow operation
- both with diffused aeration
1915 - Davyhulme, England - 100,000 gpd (approx.) at fill-and-draw
operation
- diffused aeration
1916 - Worcester, England - 2,000,000 gpd at continuous-flow
operation
- diffused aeration
1916 - Sheffield, England - 800,000 gpd at fill-and-draw
operation
- mechanical [i.e. Hayworth] aeration
1917 - Withington, England - 250,000 gpd at continuous-flow
operation
- diffused aeration
1917 - Stamford, England - 100,000 gpd at continuous-flow operation
- diffused aeration
1920 - Tunstall, England - 820,000 gpd at continuous-flow operation
- mechanical aeration
1920 - Sheffield, England - 354,000 gpd at continuous-flow
operation
- mechanical aeration
1921 - Davyhulme, England - 663,000 gpd at continuous-flow
operation
- diffused aeration
1921 - Bury, England - 360,000 gpd at continuous-flow operation
- mechanical (i.e. Simplex) aeration
In the United States, progression of the activated sludge process moved with similarly amazing speed. Edward Bartow, a Professor at the University of Illinois, visited Fowler's group in Manchester in August of 1914 and subsequently began his own bench and pilot-scale experiments along the lines established by Fowler's group.\u4,14,23\d Within a period of several months, numerous other American researchers initiated similar studies, including those by Hammond, Hendrick, Hurd, Frank, Mohlman, Hatton and Pearse.\u4,10,11,14\d Full-scale U.S. installations began to appear to 1916, according to the following listing:\u3,4,14\d
1916 - San Marcos, Texas - l20,000 gpd (approx.) at continuous-flow
operation
- diffused aeration
1916 - Milwaukee, Wisconsin - 2 MGD at continuous-flow operation
(experimental)
- diffused aeration
1916 - Cleveland, Ohio - 1 MGD at continuous-flow operation
(experimental)
- diffused aeration
1917 - Houston, Texas North Facility - 5.5 MGD at continuous-flow
operation
- diffused aeration
1918 - Houston, Texas South Facility - 5.0 MGD at continuous-flow
operation
- diffused aeration
1922 - Des Plaines, Illinois - 5.5 MGD at continuous-flow operation
- diffused aeration
1922 - Calumet, Indiana - l.5 MGD at continuous-flow operation
- mechanical aeration
1925 - Milwaukee, Wisconsin - 45 MGD at continuous-flow operation
- diffused aeration
1927 - Chicago, Illinois North Side Facility - 175 MGD at
continuous-flow operation
- diffused aeration
1927 - Indianapolis, Indiana - 50 MGD at continuous-flow operation
- diffused aeration
Comparison of the English and American installations reveals several
points of uniqueness. In England, aeration tanks were generally designed for extended detention (i.e. 8 to 12 hours) and mechanical agitation (i.e. Simplex, Hartley, Sheffield, etc.). Segmented reaeration of the recycled sludge stream was also commonplace in the belief that this assured a desired rejuvenation of the biomass. Americans considered
this latter practice as an unnecessary step, particularly given the British emphasis on extended aeration times. American aeration tanks usually provided much shorter retention (i.e. 3 - 6 hours) and were typically equipped for diffused aeration. Overall size was another American hallmark, unquestionably demonstrated by the Midwest installations.
VI. PATENT LITIGATION
Perhaps the most remarkable fact is that a rudimental bench-scale process could be transformed into multi-MGD facilities in just a matter of years. Based on its rapid growth during these first few years, it would seem that activated sludge should have become the preeminent wastewater treatment process virtually overnight. However, despite this initial intensity, activated sludge did not truly find widespread application until the 1950's.
The cause for this delay is quite simple; namely, patent litigation curtailed most of the technical momentum. Whereas Ardern and Lockett presented their research findings in May of 1914, Jones and Attwood (i.e. Jones and Attwood, Ltd.) had previously filed four separate patent applications dealing with "Improvements in Apparatus for the Purification of Sewage or other Impure Waters." These patents, their filing dates, and general coverage are listed as follows.\u24-27\d
British Patent No. 19915, Filed 11 October 1913
Subject: Wastewater aeration device based on an airlift piping system.
British Patent No. 22952, Filed 11 October 1913
Subject: Wastewater aeration based on a porous diffuser.
British Patent No. 729, Filed 10 January 1914
Subject: Wastewater treatment system based on a looped channel reactor with fluid rotation induced through a diffused aeration unit mounted in a recessed, dip chamber. Intermittent operation was employed to settle solids and decant clear top fluid, or a separate clarifier unit was used for solids recycle during continuous-flow operation.
British Patent No. 19916, Filed 11 April 1914
Subject: Wastewater aeration system based on a bottom- mounted diffuser array.
Of these four, none actually employed the term `activated sludge'. Patent No. 729 conveys the basic essence of the process, though, particularly because of its specific reference to solids recycle. Furthermore, the reactor figures provided by this latter patent bear a striking similarity to contemporary looped designs marketed by several proprietors.
Jones and Attwood must also be credited with much of the preliminary work towards establishing the practical application of activated sludge. Several of the original full-scale facilities (e.g. Worcester and Stamford) were, in fact, solely constructed at their expense and risk as a means to demonstrate its pragmatic merit. In fact, the Worcester system was designed and installed under a performance-based contract based on effluent quality.\u3,4,14\d
The patent situation for activated sludge became even more complex in 1915 when Leslie Frank, a U.S. Public Health Officer, obtained an American Patent (#1,139,024) which covered much the same material as the Jones and Attwood claims.\u28\d Frank, however, dedicated his patent for "activated slude" (the misspelling reflects Frank's terminology) to all U.S. citizens. Hence, at this point, there were two different patent entities dealing with activated sludge. Aside from these legal claims, Fowler's own standing as the originator of activated sludge was also being disputed by Clark at Lawrence.\u5,6,29\d However, despite this confusion regarding the legal status and origination of activated sludge, the American engineering community pushed ahead with its technical application.
In late 1914, Jones and Attwood, Ltd. intimated that American engineers and cities should use caution regarding patent infringements.\u30\d And when American engineers took credit for certain innovations which transgressed into their (i.e. Jones and Attwood, Ltd.) patented procedures (i.e. Hurd's announcement of the spiral-flow aeration pattern being used at Indianapolis), they were quickly rebuffed by the Jones and Attwood group.\u31,32\d But as more and more plants were built, several concern towards patent problems and complications diminished.
This mood quickly changed, though, with a suit filed by Activated Sludge, Ltd. (the licensed patentee for Jones and Attwood, Ltd.) against Chicago in the late 1920's.\u33\d Additional suits against Milwaukee, Cleveland, Indianapolis, and several smaller cities soon followed. Legal rulings on all of these cases took several years, during which time the sanitary engineering profession seriously reassessed the prospects for near-term activated sludge utilization. In 1933, District Judge Geiger ruled that Milwaukee had, indeed, violated patents held by Activated Sludge, Ltd.\u34\d An appeal was submitted, but in October, 1934 the Supreme Court declined to rule against this decision.\u35\d
In reflecting upon this outcome, Bloodgood\u36\d indicated a belief that the District Judge ruled against Milwaukee moreso because of their outspoken lawyer than the involved legal details. Whatever the case, the infringement ruling immediately rippled throughout the country. Several existing plants quickly shut down to avoid monetary fines, including the original San Marcos, Texas facility.\u37\d Many others elected to continue their use of the activated sludge process based on a royalty fee of 25 cents per capita.\u38\d Amongst the 203 activated sludge facilities identified in a 1938 Engineering News-Record inventory of U.S. wastewater treatment plants,\u39\d Kappe\d\u38\d reported that 150 were licensed by Activated Sludge, Ltd. As for the large number of communities planning to install new activated sludge plants, most simply elected either to build an alternative system (oftentimes a trickling filter) or to wait until the applicable patents expired (e.g. Washington, D.C. was a prime example).\u40\d
Milwaukee and Chicago appear to have suffered the largest losses with each being fined just under one million dollars.\u13,41\d In Milwaukee's case, these monies were secured from the proceeds on a relatively new (i.e. since 1926) sludge product, Milorganite, whose annual sales in 1934 were estimated at 3 million dollars.\u41\d In retrospect, Chicago most likely wishes it had accepted the terms of an out-of-court settlement offered by Activated Sludge, Ltd.\u13\d Indeed, rather than paying for the imposed fine and several years of legal involvement, they could have reconciled their case with a $90,000 payment.
VII. ADDITIONAL CONTROVERSY
This era of legal controversy (circa 1915 to 1935) was also marked by two other topics of intense technical debate. The first dealt with the choice of aeration systems and whether it be diffused or mechanical in form. The second debate centered around the fundamental behavior of the process, in terms of physical-chemical versus biological mechanisms.
The aeration question was a significant concern from the very beginning and one which evoked bitter debate. Even the earliest activated sludge researchers were keenly aware that the requisite energy demand would play a dominant role in determining the cost-effectiveness of the process. On the one hand, several investigators believed that all oxygen transport occurred at the liquid surface, such that mechanical aeration served as the optimal gas transfer mechanisms (Buswell\u42\d, Peck\d\u43\d and Kessener and Ribbius\d\u44\d ). This view was countered by another group which regarded diffused aeration as the ideal system (Fowler and Chaterjee\u45\d, Roe\d\u46\d, Nordell\d\u47\d and Keefer\d\u48\d). In a classic series of three articles published during 1936 and 1937, however, Ridenour and Henderson\u49\d thoroughly explored each option and concluded that either had its particular merits or demerits. Although they indicated that a mechanical unit might provide nominally higher gas transport at an equivalent energy demand, the selection was judged to be a site-specific factor.
The second major debate revolved around the fundamental activated sludge mechanism; whether it was a physical-chemical operation or a biological process.\u48,50\d Baly theorized that differential charging between sewage colloids and floc matrixes resulted in an electrostatic attraction and consequent clarification.\u48\d Along similar lines, Theriault considered the activated sludge process as a biozeolite mechanism.\u48\d Numerous other researchers believed that iron compounds played a dominant role in the oxidation process\u48\d. This concept was likely stimulated by the original M-7 research conducted by Fowler and Mumford. Subsequent refinement to this premise held that the iron functioned as an oxygen carrier to facilitate subsequent oxidation.\u51\d
In terms of the biological premise, enzyme activity was initially regarded by many investigators as the primary mechanism (Harris et.al.,\u52\d Woolridge and Standfast,\u53\d Mohlman\d\u54\d). Cramer\d\u55\d considered protozoan metabolism to be the fundamental agent, while Eisenberg concluded that protozoa served mainly to indicate desirable activated sludge composition.\u48,50\d Ardern\d\u56\d also regarded protozoa as a quality indicator, with an additional belief that they facilitated improved effluent clarity. Buswell's\u50\d analogy for activated sludge is undoubtedly the most pithy, though, comparing its activity to `hungry hogs'. By 1920, research conducted by Buswell and Long\u57\d had essentially verified the biological mechanism behind activated sludge. However, Mohlman's 1930 editorial\u58\d still expressed a serious lack of fundamental knowledge regarding the activated sludge process.
VIII. PROGRESSIVE REFINEMENT
Over the years, several refinements and/or modifications to the activated sludge process have been devised with the intent of promoting better performance. These improvements were oftentimes developed to economize on the use of aeration. Jones and Attwood\u59\d probably initiated this latter pursuit with their interesting patent in 1916 based on the use of intermittent aeration. Their design employed a novel mechanical valve assembly which effected cyclic periods of on-off aeration, such that the net aeration demand was reduced from that of a constant supply. This practice has, coincidentally, been resurrected in recent years in an attempt to incorporate nitrification and denitrification into a single-tank activated sludge system.\u60\d Further research on reducing the aeration demand consequently led to tapered aeration in 1936,\u61\d step aeration in 1942,\u62\d and modified aeration in 1943.\d\u63\d
Beginning in the late 1920's, another group sought to intensify the treatment capacity by coupling attached biomass growth with the suspended-growth activated sludge process.\u9\d Generally known as submerged contact aerators or aero-filters,these aerated systems provided additional wooden laths or brushwood surfaces for the desired biofilm growth. These latter studies by Imhoff\u64\d and Clark\d\u65\d were essentially a continuation of the classic Black and Phelps\u15\d research previously conducted at New York. Perhaps the most widely used system of this kind was the Hays Process.\u66\d Originally developed in the 1930's, the Hays design used corrugated asbestos-concrete sheets vertically stacked within the aeration tank.\u9\d Although employed extensively at U. S. military installations in the 1940's,\u67\d popularity of the process faded during World War II. Wartime material shortages required the substitution of flat sheets which were prone to buckling and collapse.\u37\d
As with the intermittent aeration concept, this latter technology also has its contemporary offspring. Philadelphia, for example, has successfully mated rotating biological contactors with their existing activated sludge reactors.\u68\d And a currently marketed proprietary design, Cytox, essentially provides much the same treatment scheme as the Hays process.\u69\d
Further innovations through the 1940's and earlier 50's resulted in the Kraus and biosorption processes.\u7,8\d In 1944 alone, there were two further additions to this growing list of process modifications, including high rate treatment\u70\d and the `Z' process.\d\u71\d Although the former option is currently well recognized, the `Z' process has faded into obscurity, and for good reason. With the intent of promoting enhanced floc sedimentation, the `Z' process continuously dosed the aeration tank with asbestos fibers.
Pasveer's\u72\d documentation of an intermittent oxidation ditch system in 1954 proved to be a significant revelation since fill-and-draw operation had not been used for a number of decades. In fact, only six years before Pasveer's publication, Imhoff\u73\d vehemently denounced the use of intermittent/fill-and-draw cycling as a thoroughly unsuitable procedure. In our contemporary literature, however, the sequencing batch reactor concept proposed by Irvine\u74\d has now taken the initiative towards periodic operation. Indeed, a study is now underway to explore the coupling of intermittent aeration, fixed-film treatment, and batchwise processing in a multi-faceted resurrection of yesteryear concepts.\u75\d
Despite Sawyer's\u8\d inference that the activated sludge process had been thoroughly covered, ongoing research in the field has continued to make significant advancements over the past decade. Process automation using advanced control instrumentation and analyzers has made, and will continue to make, substantial progress in process optimization. And the subject of biological phosphorus uptake, only recently transferred from the realm of black art to pragmatic reality,\u76\d will certainly draw intense consideration in the coming years.
IX. SUMMARY
This inspection of the yesteryear literature on activated sludge will hopefully provide a beneficial perspective on our current state-of-the-art. Once patented as activated "slude" and considered analogous to hungry hogs, the activated sludge process has undergone seven decades of colorful evolution since Fowler originally acquired his "illuminating idea" at Lawrence in November, 1912. Perhaps the most enlightening conclusion which might be drawn in consideration of recent events is the obvious reinforcement of an inescapable fact that history does repeat itself.
ACKNOWLEDGEMENT
This paper was presented at the 55th Annual Conference of the Water Pollution Control Federation on 7 October 1983 in St. Louis, Missouri. Correspondence can be directed to J. E. Alleman, School of Civil Engineering, Purdue University, West Lafayette, Indiana 47907.
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