ES&T
OUTLOOK
Fixed-film filtration This wastewater treatment technique reputedly forms less sludge; some approaches may even produce energy
Interest in fixed-film biological (FFB) processes for wastewater treatment continues high, because of their perceived advantages over suspended-growth or activated-sludge systems. Essentially, an FFB process involves contact of the wastewater with a film of diverse microorganisms_/wed or attached to natural or synthetic media. Conditions can be either aerobic or anaerobic (ES&T, July 1982, pp. 380-84A), depending on treatment goals. Two principal developments have made the FFB process a viable option—the development of new process configurations for trickling filters and the rotating biological contactor (RBC) process. Generally, aerobic fixed-film systems such as the RBC require less energy, produce less sludge, are less costly, and are simpler to operate than activatedsludge systems. The newer RBCs are in use at 236 municipal plants as of 1982. In a few selected cases, EPA has accorded aerobic processes using RBCs "innovative and alternative" (I&A) status under the Construction Grants Program. However, more research is being concentrated on anaerobic approaches because if certain problems can be surmounted, they would use even less energy and make far less sludge than their aerobic counterparts. Indeed, they may produce enough energy, in the form of methane gas, to run a plant and, under optimum conditions, even have enough left over for other purposes. Continuing problems, progress, and prospects for both aerobic and anaerobic systems were discussed at the Second International Conference on Fixed-Film Biological Processes, organized by the Uni310A
Environ. Sci. Technol., Vol. 18, No. 10, 1984
versity of Pittsburgh and other sponsors and convened at Arlington, Va., in July. Metal toxicity What happens when metals impinge on an FFB process? The toxicity de-
pends on the type, total concentration, and soluble concentration of the metal, and on the type of biosystem, Ju-Chang Huang of the University of Missouri (Rolla) explained. For instance, an aerobic system is less sensitive than an an-
© 1984 American Chemical Society
0013-936X/84/0916-0310A$01.50/0
aerobic one; heterotrophic microbes are less sensitive than autotrophic microbes. Moreover, he observed, a slow applica tion of a metal causes less system disrup tion than does a shock loading. Huang tried applications of copper(II) and cadmium(II) on an RBC system. He applied 5 mg/L of cadmium(II) for 24 h, for example, and observed a drop in BOD degradation efficiency from 92% to 82%; however, after seven days, the system recovered to 90% efficiency. Huang also tried 20 mg/L over 72 h. Efficiency was "depressed" for five days, after which recovery occurred. He reported parallel results with copper(II). "Maybe the microbial system developed some tolerance after the first cadmium 'spike,'" Huang suggested. Removing pesticide material Larry Moore of Memphis State Uni versity (Tenn.) observed that "there are few disposal alternatives" for hazardous wastewaters, but expressed optimism that RBCs with sludge recycle "would work." He tried such a system to break down a pesticide formulation wastewa ter, achieving significant removal of the emulsifier and the pesticide itself. To develop the biomass, Moore used commercial dog food. He then began to acclimate the system to the pesticide ma terials by gradually increasing the amount of formulation waste. Moore described initial difficulties in getting the system to sustain an 80-85% COD removal, but said that later, higher mi crobial forms—particularly protozoa— could be retained, and difficulties sur mounted. Among materials he tested were chlordane, endrin, heptachlor, and copper(II). Improving anaerobic performance Pete Podolak of Syracuse University (Ν. Υ.) suggested that excessive concen trations of off-gases, such as hydrogen, hydrogen sulfide, and carbon dioxide, may accumulate at cell sites within the anaerobic biofilm. There, they may physically interfere with the transport of substrate to the microbial surfaces, block the removal of metabolic waste products from cells, or do both. Local increases in the concentration of these gases may result in product inhibition or accumulation to toxic limits, unless the liquid phase solubility of such gases were reduced. Podolak used a synthetic wastewater consisting of sucrose as the sole organic carbon source to investigate the effects of reduced headspace gas pressures on an anaerobic RBC. He reported sub stantial improvement in COD removal rates for high-organic loading condi tions under vacuum pressure opera tions. Moreover, Podolak observed ac
celerated cellular growth, apparently resulting from more efficient microbial substrate utilization under these condi tions. He said these results indicate that reduced pressure operations can signifi cantly improve the performance of or ganically overloaded systems and may enhance anaerobic reactor start-up. Some research needs Optimization of the availability, relia bility, and productivity of anaerobic FFB systems remains a principal re search goal. Nevertheless, even though aerobic systems are in more widespread use, their research needs should not be ignored. For example, Denny Parker of Brown and Caldwell (Walnut Creek, Calif.) spoke of hopes for improved filter media designs. He said that the real challenge will be to design media to meet new specifications as more sophis ticated wastewater systems, needed to handle toxic and hazardous materials, come into being. Parker spoke of the need to find ways of developing media with improved oxygen transfer effi ciency, as well as process kinetics de scriptions useful to consulting engineers for design purposes. Parker told ES&Tthat his firm devel oped a new approach to the old trickling
filter process, which involves the recir culation of sludge to an aerated solids contact tank downstream of the filter. "Incorporation of dispersed trickling filter solids into floe [bioflocculation] results in a crystal clear effluent from the process," Parker said. He added that this technique was first applied at Corvallis, Ore., in 1979 and is now being used at 40 locations in the U.S. —Julian Josephson
Additional reading Fixed-Film Biological Processes for Wastewater Treatment. Yeun C Wii. Ed D Smith. Eds. 493 pages. Noyps Data Corp Mill Rd at Grand Ave Park Ridge Ν J 07656 1983 S48, hardcover This book contains selected pa pers from the 1480 and 1982 confer ences on fixed-film processes, plus additional studies which provide a re view of these processes under differ ent aerobic and anaerobic conditions with various types of media and con tactors
nai
...SATISFIES YOUR PROIECT NEEDS WITH
ENVIRONMENTAL SCIENCE & ENGINEERING/ SERVICES •••.•• .
»ΐ»».
- Air Q u a l i t y M o n i t o r i n g / M o d e l i n g > : • Hazardous W a s t e E v a l u a t i o n / M a n a g e m e n t • Ground W a t e r Investigations . • ^ • R e g u l a t o r y Compliance Audits.^ .:.£/· > ί - . ν ^ ^ • Environmental Impact Studies " *~' ' "·' H y d r b p o w e r 'Environmental Studies... ^ -·• Permit Assistance: RCRikNPDEtf,*rçS0* v - - .._ - ^ - ^ K ^ 3 j M ^ ^ ^ > , N.H.
