Lem Tec Biological Treatment Process

The LemTec™ Biological Treatment Process uses the LemTec™ Modular Cover to completely cover the system rather than a mat to retain duckweed (Figure 4.26). The process is still a lagoon-based treatment process composed of a series of aerobic cells followed by an anaerobic settling pond. Cells in series consist of a complete-mix aerated reactor, a partial-mix aerated reactor, a covered anaerobic settling pond, and a Lemna polishing reactor. The polishing reactor is aerated and has submerged, attached-growth media modules to supplement BOD and NH3-N reduction. Sludge removal from the settling pond is expected to be required about every 5 to 12 years. Frequency of cleaning will vary with climate and strength of the wastewater.

Primary and Secondary Treatment Stage

Polishing/Tertiary Treatment Stage

FIGURE 4.23 Flow diagram for a typical Lemna system. (Courtesy of Lemna Technologies, Inc., Minneapolis, MN.)

Preliminary Treatment Lemna Treatment Zone

Preliminary Treatment Lemna Treatment Zone

FIGURE 4.24 Flow diagram for Lemna system application. (Courtesy of Lemna Technologies, Inc., Minneapolis, MN.)

Location: Northern Georgia

FIGURE 4.24 Flow diagram for Lemna system application. (Courtesy of Lemna Technologies, Inc., Minneapolis, MN.)

Lemna Polishing Lagoon ^

Lemna Polishing Lagoon ^

FIGURE 4.24 (cont.)

Floating Barrier Grid

Floating Barrier Grid

Location: Southern Nevada

Lemna Treatment Lagoon

Lemna Polishing Lagoon

Bar Screen and Grit Removal

Lemna Polishing Lagoon

Bar Screen and Grit Removal

Wastewater

Floating Barrier Grid

Wastewater

Floating Barrier Grid

Location: South Central Poland

Wetland Buffer

Lemna Tertiary Polishing Lagoon

Floating

Barrier

Grid

Floating

Barrier

Grid

Location: Northern North Dakota

FIGURE 4.25 Photograph of Lemna harvesting equipment and floating barrier grid. (Courtesy of Lemna Technologies, Inc., Minneapolis, MN.)

4.10.4 Las International, Ltd.

Accel-o-Fac™ and Aero-Fac™ systems are offered as upgrades and original installations. Accel-o-Fac™ is a facultative pond with wind-driven aerators, and Aero-Fac™ is a partial-mix aerated lagoon utilizing an Aero-Fac™ diffused air bridge and LAS Mark 3 wind and electric aerators. Systems have been installed in several countries including Great Britain, Canada, and the United States. Performance data are limited, as with most lagoon systems, and data presented in the company literature are primarily limited to operation during warm months

TABLE 4.16

Typical Effluent Qualities Expected from Lemna Systems

TABLE 4.16

Typical Effluent Qualities Expected from Lemna Systems

Parameter

Influent

Effluent

BOD (mg/L)

250-200

<30-10

TSS (mg/L)

300-250

<30-10

TN (mg/L)

80-40

<20-5

NH3-N, (mg/L)

50-10

<10-2

TP (mg/L)

20-10

<1

LemTec™ Biological Treatment Process

LemTec™ Biological Treatment Process

FIGURE 4.26 LemTec™ Biological Treatment Process. (Courtesy of Lemna Technologies, Inc., Minneapolis, MN.)

of the year. Winter performance data are limited but are necessary to evaluate the processes; however, it is expected that the systems will perform essentially as other partial-mix lagoon systems with equivalent aeration. The advantage of the processes is a savings in power costs if adequate wind velocity is available. A disadvantage of the Accel-o-Fac™ is the lack of control of the aeration process.

4.10.5 Praxair, Inc.

The Praxair® I-SO™ systems have been installed in over 100 locations throughout the world (Figure 4.27). Each unit is capable of transferring 240 lb oxygen per hr. Praxair has reported that the total power required to operate the Praxair® I-SO™ System, including the generation of oxygen, is as much as 60% less than the air systems replaced. Plants located near an oxygen pipeline supply can decrease power costs up to 90%.

4.10.6 Ultrafiltration Membrane Filtration

In 2001, John Thompson Engineering of New South Wales, Australia, designed and installed a 0.264-mgd (1000 m3/d) Zenon membrane facility to polish an effluent from a lagoon facility. Operating data are not available, but all indications are that the facility is functioning well. Very little operating experience is available with membranes in lagoons, but it is an option that should be evaluated.

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