Section 01 - Introduction

01.a Purpose

The Marine Park Water Reclamation Facility (MPWRF) is an activated sludge, secondary treatment plant. The plant treats municipal and industrial wastewater from the City of Vancouver, Washington. The plant removes organic and suspended material from the waste stream to the level provided by secondary treatment. The wastewater is disinfected before it is discharged into the Columbia River. Sludge is collected and pumped to the Southside Interceptor which drains to the Vancouver West Side Wastewater Treatment Plant.

Wastewater characteristics and design criteria for the plant are as follows:

01.b.1 Collection System

The collection system area covers approximately 52 square miles. The system is divided into three basins defined as the Westside, Marine Park and Diversion Basins (see Figure 01.08).

Wastewater from the Westside and Marine Park Drainage Basins are directed to their respective treatment facilities. The Diversion Basin, through Burnt Bridge Pump Station, can divert flows to either the Westside or Marine Park Basin.

01.b.2 Plant Location

MPWRF is located on a 23-acre site 2 miles east of the I-5 freeway on the Columbia Parkway, just north of the Columbia River (Figure 01.03. The site is bordered on the west by the Portco light industrial property, to the north by Burlington Northern Railroad tracks and State Route 14, to the east by undeveloped wetlands owned by Tidewater Barge Lines and to the south by Marine Park. A plant site plan is shown in Figure 01.04.

Figure 01.05 shows a schematic view of the plant process wastewater flow patterns. Each process is described in detail below.

01.b.3 Solids and Liquids Balance

Figure 01.05 also shows the Plant Liquids and Solids Process Balances. Each balance/schematic describes the major process flow streams and lists the hydraulic, organic, and solids loading rates under various conditions.

01.b.4 Hydraulic Profile

The hydraulic profile for the plant is shown in Figure 01.06 for several operating conditions.

01.b.5 Influent Pump Station

Wastewater enters the influent wetwell through a 48-inch interceptor. Five influent pumps pump the wastewater from the wetwell to the plant influent channel. All five pumps are vertical, dry-pit, non-clog, centrifugal pumps with adjustable frequency controlled speed.

01.b.6 Screenings Facility

The wastewater is pumped through a combination of three mechanically-cleaned and one manually-cleaned bar screen designed to remove rags, plastics material, and other large solids. The solids material from the bar screens, called "screenings," is then conveyed to two screenings presses where it is dewatered and conveyed to the screenings/grit container(s) for disposal.

Each bar screen has a Parshall flume located downstream of it. The Parshall flume controls the water level and flow velocity through the screens and is also used for flow measurement.

01.b.7 Grit Removal

After the wastewater flows through the Screenings Facility, it enters one or more of the three aerated grit chambers. Heavier solids such as sand, grit, and gravel (or other solids that have higher settling velocities than many of the organic solids) settle out on the bottom of each chamber. The wastewater exits the grit chambers and enters and aerated channel connecting to six primary clarifiers.

The grit collected into the hoppers from the grit chambers is pumped by nine pumps to three cyclone grit separators. Three inclined screw grit classifiers further separate the grit from the wastewater before it falls into a disposal container.

01.b.8 Primary Treatment

After preliminary treatment, the wastewater flows through an aerated channel to six rectangular primary clarifiers. The quiescent conditions in the clarifiers cause suspended materials in the wastewater to settle to the bottom of the tanks and collect there as primary sludge. The primary sludge is then pumped by six primary sludge pumps to the existing Southside Interceptor. The primary effluent flows from the primary clarifiers to the Aeration Basins.

Scum, which is lighter than water and floats to the surface of the clarifiers, is collected and pumped via the primary scum pump to the existing Southside Interceptor.

01.b.9 Activated Sludge Process

Primary effluent flows into the six aeration basins. Each basin has an anoxic and aeration zone. This allows the operator to provide nitrification/denitrification along with the standard BOD removal in the basins. The primary effluent mixes with the activated sludge in the aeration basins in the presence of air provided by four multi-stage centrifugal blowers. The microorganisms in the activated sludge use the soluble and insoluble organics in the wastewater as a source of energy for growth and reproduction. The microorganisms use oxygen for the conversion of the organics for this growth and reproduction. In this manner the organic wastes are converted into a microbial suspension which then flows through the basins and over the discharge weir by gravity to the secondary clarifier splitter box. The splitter box controls flow to the four secondary clarifiers.

The four circular secondary clarifiers provide a quiescent environment similar to the function of primary clarifiers that permits scum to float to the surface and flocculated sludge to settle to the bottom. Baffle skirts at the entrance to each clarifier impart a downward velocity to the mixed liquor, thereby aiding a quick precipitation of the sludge. A collector mechanism, called a "rake-arm", sweeps the floor of each clarifier in a circular motion, and the sludge thus collected is pumped by the return activated sludge (RAS) pumps back to the activated sludge basins.

A polymer system is available to provide polymer to aid in settling.

The scum that rises to the surface is swept to troughs by a rotating scum skimmer. The scum and waste sludge is pumped to the Southside Interceptor.

01.b.10 Ultraviolet Disinfection

After secondary treatment, the secondary effluent then flows to the six ultraviolet (UV) disinfection channels where UV light is used for disinfection. After primary treatment, secondary treatment, and finally disinfection, the treated effluent flows by gravity through a Parshall Fume for flow measurement to the outfall diffuser and into the Columbia River. In the event of certain combinations of high river elevations and high plant flows, three effluent pumps pump to the outfall diffuser.

01.b.11 Solids Handling

Approximately six yards of grit and screenings are removed per week from the waste stream and hauled to the landfill. Primary Sludge and Scum and Waste Secondary Sludge and Secondary Scum are pumped to the Southside Interceptor which flows to the Vancouver West Side Wastewater Treatment Plant. There the solids are blended with West Side solids and eventually incinerated.