Sludge processing and disposal has become a serious dilemma leaving plant managers, developers and municipalities with only limited options. Landfills are running out of room, regulatory agencies are imposing more stringent restrictions on disposal, and the processing and disposal costs are skyrocketing.

New Option to Sludge Problem

A new means of tackling the sludge problem was unveiled recently at WEFTEC 2002 by Premier Wastewater International (PWI), based in Nevada. Termed the Enhanced Solids Reduction (ESR) process, this innovative wastewater treatment system is an advanced activated sludge process that can reduce organic sludge up to 90%. It does so by conditioning the entire waste stream, oxygenating and altering its state to greatly enhance the efficiency of the natural biological processes responsible for stabilization and removal of unwanted constituents.

The heart of the ESR process is the proprietary Multi-Action Conditioner (MAC) system combining a superior aeration process with an aggressive blending of the waste stream's components. Through the effective use of hydraulics, the MAC violently mixes atmospheric air and mixed liquor under pressure generating micro-bubbles, shearing, and selective cavitation. The complex associated forces fractionalize the particulates and shear larger oxygen bubbles into micro and micron-sized bubbles and makes nutrients and oxygen more available to microorganisms.

In addition, under ordinary circumstances, an oxygen concentration gradient in floc makes it aerobic on the outside, but anaerobic towards the center. With the MAC, the micro- and micron-sized bubbles become entrained inside the floc, keeping it totally aerobic over time.

The hydraulic activity that takes place in the MAC and elsewhere in the ESR process blends the entire waste stream into a relatively uniform biota consistency. The microorganisms, nutrients and oxygen are brought into intimate contact with each other and maintained in that state. The microorganisms are then taken into a high level of endogenous respiration in which they consume cellular materials and other nutrients at an expedited rate. The subsequent enhancement in biological processing is evidenced by a typical ESR decay coefficient that is twice the conventional level (see Figure 1).

ESR Process Demonstration Plant

PWI has been testing the MAC system and ESR process in both municipal and industrial applications for over four years. Most recently, the company built a demonstration plant in Mesquite, Nevada designed to treat 100,000 gallons of municipal wastewater per day and provide reuse quality effluent that would meet California's stringent Rule-22 discharge requirements.

The demonstration plant consists of two ESR process tanks with a working capacity of 5,800 gallons each. Two additional tanks, one anaerobic and one anoxic, are used for phosphorus removal, nitrification and denitrification. Typical headworks, clarifier, sand filter and chlorine contact basin complete the plant design. Settled solids from the clarifiers and the filter backwash water are returned to the ESR process tanks for further processing. Traditional primary treatment is not necessary with a new ESR installation.

In the first 10 months of operations, the plant processed over 15 million gallons with no intentional wasting and reduced the organic solids in excess of 90%. Because of its flexibility, the ESR process can be designed to achieve virtually any level of organic sludge reduction. Like any activated sludge plant, the ESR process is designed for periodic wasting of the inerts, however infrequent.

Certified laboratory results verify that during a lengthy test period at the plant the ESR process significantly reduced biochemical oxygen demand (BOD5), total suspended solids (TSS), and ammonia (see Figure 2). It also decreased the total Kjeldahl nitrogen (TKN) levels to below 1 mg/L, which reflects a significant reduction in organic nitrogen compared to traditional activated sludge processes. In addition, the ESR process proved itself to be ideal for biological removal of other unwanted wastewater constituents including phosphorous and nitrogen.

The ESR process achieved these results without using any chemical additives (except chlorine for disinfection), flocculants, manufactured microorganisms, enzymes or other additives. The test reflects a mean-cell residence time (MCRT) ranging between 60 days to over 2,000 days with an average of about 80 days. The low net-sludge production and long MCRT indicates a nearly complete volatilization of organic matter. The loading range (food-to-microorganism [F/M] ratio) averaged 0.1 to 0.65 indicating a conventional- to high-rate process loading range. The dissolved oxygen (DO) levels ranged from between 2 mg/L to 3.5 mg/L. The plant operated best at mixed liquor suspended solids (MLSS)
Got Sludge? continued from page 4 concentrations ranging from 2,400 mg/L to 3,200 mg/L although it would process MLSS as high as 5,000 mg/L.

Industrial Case History

The MAC system and ESR process have also been tested in industrial applications with excellent results. A juice concentrate plant in Southern California was experiencing significant noncompliance fines and high operating costs. The plant was processing 100,000 gpd with an influent BOD of 3,600 mg/L and the discharge permit required the BOD to be less than 250 mg/L. The juice company tried several different aeration systems but the lowest BOD they could achieve was 2,600 mg/L using a 60-hp motor and large amount of expensive defoamer to keep from burning up the motor. Faced with the prospects of an expensive redesign of the entire treatment plant, the plant installed a MAC system. Within 72 hours of installation, the MAC system using a 15-hp motor reduced the BOD to less than 900 mg/L.

Once the plant operator could properly manage the microorganism colony, the plant was totally compliant within 30 days. Later, an additional 15-hp MAC system was installed to increase capacity to as much as 175,000 gpd. This increase was gained without major expansion or expense. After four years of operation at this location, the only upkeep required was normal pump maintenance. Except for the motor and pump, the MAC system has no moving parts. Because its components are located on the tank's exterior, any maintenance is normally quick and simple with minimal impact on processing.

Design and Operational Flexibility

The ESR process is highly scalable with a great deal of process design and operational flexibility. Any of the typical design parameters for activated sludge processes can be used including complete mix, plug flow, contact stabilization, step feed and extended aeration. It can also work in cold, temperate or hot climates.

The ESR process can be used as part of a new treatment facility, as a retrofit into an existing facility or as a stand-alone side-stream digester. Aerating the influent waste stream immediately reduces odors. The entire waste stream is taken from the headworks or grit basin directly into the ESR tank(s) where it is circulated through the MAC system. It is then sent to a clarifier where the solids are settled and returned to the ESR for further processing. If required, anoxic and anaerobic tanks can be added for nitrification and denitrification as well as phosphorus removal. Depending on discharge requirements the cleaner ESR effluent can be sent through filters and/or a disinfection process similar to traditional systems.

ESR Process Advantages

One of the primary advantages of the ESR process is cost savings both in construction and operations. The ESR process can eliminate the need for primary systems, lagoons, odor-control equipment, scrubbers, blowers, sludge-handling equipment and many other components associated with traditional systems. As a result, capital costs can be reduced 20% to 40%. In addition, because of reduced odors, noise and misting, the buffer zone surrounding an ESR plant is much smaller or can be eliminated completely where regulations permit. Installation can be done relatively quickly, and in the case of retrofits, does not significantly inhibit ongoing operations. Its simplicity also leads to ease of maintenance.