By Manuel Alvarez Cuenca, Eva Maria Palomero, Rakesh Desai & Ana Maria Escribano

Introduction
A joint project between Aqualia and Water Purification Technologies, Inc., was created to test an advanced, compact effluent treatment unit. The municipal wastewater of the city of Toledo, Spain, consists of a mixture of domestic and industrial wastewater, landfill leachate and septic tank effluent. The staff of the plant carried out the installation, maintenance and chemical analyses required to evaluate the performance of the system. The performance evaluation lasted for more than one year and was completed in March 2006.

Installation, land requirements, operation and maintenance
The unit was partly assembled in Toronto, Canada and shipped to Spain. Three plant operators, not previously familiar with the unit, carried out both the installation and start-up in less than 12 hours. It was placed between the grit chamber and the primary settling chamber of the plant. As a result, the wastewater entering the unit had no primary treatment.

The unit has low space requirements; in the present case for a treatment capacity of six m3/day (211.89 ft.3/day) of domestic wastewater, the footprint required is 2.9 m x 2.3 m (9.51’ x 7.55’). Units with larger capacities will, of course, require larger footprints.

The labor costs are equally modest in terms of skills required from operators, minimum supervision and maintenance costs. For example, the maintenance time spent by the operators seldom exceeded two hours per month.

Characteristics of the wastewater treated
As indicated above, the municipal wastewater treated in Toledo consists of a mixture of domestic and industrial wastewater from the food industry, leachate from landfills and seepage from septic tanks. The ratio BOD5 /COD is customarily adopted as an indicator of a biological treatability of the wastewater1; values of 0.8 and above indicate easily biodegradable wastewater. As shown in Graph 1, the wastewater treated in Toledo most of the time exhibited values between 0.4 and 0.5; that is, wastewater difficult to treat biologically. A ratio of 0.3 (observed in April 2005) indicates a toxic shock. (Toxic shock is a surge in the amount of toxic chemicals reaching the secondary treatment. As a result, the biomass responsible for the treatment of contaminated water is destroyed or poisoned. The process must be stopped and restarted.) Indeed, maintenance work scheduled at several locations in the municipal plant, especially in the raw sewage collector, produced concentrations of ammonia exceeding 110 mg/L.

Between March and April, the plant experienced a series of upsets and unstable chemical loads reflected by the strong increases in COD relative to the concentration of BOD5. The unit recovered quickly from these toxic shocks and maintained the high removal performance expected until the end of the evaluation program in December 2005. Flow rates ranged from 3,000 L/day (792.52 gal/day) to 7,000 L/day (1,849.20 gal/day). Much larger flows of up to 1,000 m3/day (35,314.66 ft.3/day) can be treated by installing these modules in parallel.

Characteristics of the technology
The technology is based on both the mass transfer characteristics of fluidized-bed bioreactors and the high-interfacial area of the proprietary RBC media. The units are highly compact and the treatment capacity of individual modules ranges from three m3/day (105.94 ft.3/day) to 100 m3/day (3,531.47 ft.3/day). They can be manufactured in concrete, steel or fiberglass and can treat high-strength wastewater with BOD5 removal performance >95 percent as verified by the Ontario Ministry of the Environment (Canada). Graph 2 and Table 1 exhibit the removal performance of the tested unit in treating high-strength winery wastewater.

Performance results
Before discussing the results, it must be pointed out that the unit treated effluent from the grit chamber without primary settling. This, added to the low biological treatability of this particular wastewater (resulting from the addition of landfill leachate and bottoms of septic tanks) made the test far more severe.

The evaluation of the technology had two distinctive phases. In the first phase, lasting from March to April 2005, the plant underwent a series of scheduled repairs and modifications, which produced high levels of COD and chemical shocks as a result of the alterations in the collection of raw sewage. These unstable conditions delayed the growth of the biofilm, which takes approximately one month. Once stable operating conditions were resumed by the middle of June 2005, the biofilm established itself and the unit performed to the set standards and to complete satisfaction.

Meeting or exceeding the objectives proved the unit’s suitability. In that respect, it compares very well with the removal performance of large municipal plants like those in Niagara Falls, Ontario, and Toledo (see Table 2).

BOD5 removal performance
Graph 3 shows a consistent 90 percent removal of BOD for the six-month period June to December 2005. During that period (September to November), the wastewater exhibited a BOD5/COD of less than 0.4 indicative of low biological treatability. The unit tested has a treatment capacity of 6,000 L/day (1,585.03 gal/day) with domestic effluent. The BOD5 removal efficiency obtained in Toledo for this type of wastewater was 90 percent. The design performance parameter of the unit, with more easily treatable wastewater such as conventional domestic wastewater, is 95 percent.

TSS removal
The set objective for total suspended solids removal was 85 percent. The results achieved in Toledo were 88 percent. As shown in Graph 4, the trends observed during the nine-month operation of the unit coincide with the events explained above. Because of the unit’s high performance, very moderate amounts of sludge were produced and its removal was accomplished via simple manual operation.

Ammonia performance removal
The performance evaluation established did not include ammonia removal as a set objective. As noted previously, the concentration of ammonia in the municipal effluent was often up to fives times higher than that typically found in wastewater. Ammonia concentration in the influent to the unit at one point exceeded 110 mg/L. The results shown in Graph 5 confirm the excellent nitrification performance of the unit with an average of over 95 percent removal through the six-month period during which the plant had stable operation.

Comparative performance
Although comparing the performance of a compact, decentralized unit with a full-scale municipal plant is not always possible, to do so gives a good indication of the overall efficiency of the new unit. This is shown in Table 2. The performance data from the Niagara Falls Municipal Plant and that of the city of Toledo Municipal Plant was graciously made available by both plants.

In the last column of Table 2, the comparison is between the performance of the trickling filters used in Toledo as the bioreactors for secondary treatment and the unit. It deserves to be stressed that the effluent treated by the unit is less amenable to biological treatment than those with primary treatment like conventional municipal plants; the results obtained compare very well with those achieved in both facilities.

Conclusions
The technology performance has been verified by Environment Canada (ETV program) and the Ontario, Canada, Ministry of the Environment (MOE). From the results obtained, we can draw the following conclusions:

  • The new unit met and exceeded the preset goals established for the technology performance evaluation.
  • The removal efficiency for BOD5, TSS and ammonia were 90 percent, 88 percent and 95 percent respectively.
  • The operation and maintenance demanded by the 6,000 L/day (1,585.03 gal/day) unit was less than two hours per month.

Reference

  1. Metcalf & Eddy, Wastewater Engineering: Treatment, Disposal and Reuse, Fourth Edition, 2003, McGraw-Hill Book Co., New York. (See Wastewater Engineering, page 96.)

Special acknowledgements
Ximena Correa of Water Purification Technologies Inc., Toronto, Canada for her excellent job organizing, collecting and setting the evaluation data. Adrian Rodriguez, Aqualia, EDAR, Toledo, Spain, for his superb professional dedication during the installation, monitoring and maintenance periods. Miguel Angel Alonso, Aqualia, Madrid, Spain for his technical observations during the plant operation.

About the authors
Manuel Alvarez Cuenca, Ph.D., P.Eng is CEO and President of Water Purification Technologies Inc. and President of Ecotechnos Inc.(www.ecotechnos.com), both located in Toronto, Canada. Ecotechnos Inc. designs advanced wastewater treatment units for industrial and domestic wastewater for small and medium sized business primarily in the viniculture, dairy and agricultural industries as well as municipal wastewater. Cuenca has more than 30 years of experience in wastewater treatment and has published numerous articles and treatises, including a book on fluid technologies. Cuenca is a professor and director of the Water Treatment Technologies Laboratory at Ryerson University, Toronto, and a recipient of the Canadian Ministry of the Environment’s Global 2004 Award for Aquacan 5000 for the treatment of winery wastewater. Eva Maria Palomero, EDAR, Aqualia,Toledo, Spain; Rakesh Desai, Water Purification Technologies Inc., Toronto, Canada; Ana Maria Escribano, EDAR, Aqualia, Toledo, Spain contributed to the article. All correspondence should be addressed to Cuenca at mcuenca@ecotechnos.com as corresponding author.

About the company
Water Purification Technologies (WPT) is a Canadian company involved in the manufacturing and commercialization of advanced and cost-effective wastewater treatment package plants designed by Ecotechnos Inc. (Toronto). WPT manufactures AQUACAN® modular units of 3, 6, 15, 30 and 50 m3 /day, and can treat industrial effluents of over 15,000 mg/L BOD5 and ammonia with over 90-95 percent removal efficiency.

 

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