Process
Screenings Removal
The wastewater passes through an Aquaguard Screen® removal system which uses bar screens to remove large debris which could damage plant equipment, located further downstream. This debris is cleaned and hauled to an approved land fill.
Primary Clarification
The clarifier slow the flow allowing heavy particles to settle to the bottom of the clarifier tank. The solids or sludge are pumped to the sludge thickener for further treatment.
Biofiltration
The biofilter continually distributes water from the clarifiers over rocks which provide a home for microorganisms that break down organic material into simpler inorganic chemicals. The biofilter conditions mimic the environment of rocky stream beds and ocean coasts.
Biotower-Nitrification
The biotower distributes the water over sheets of corrugated plastic (Cross-Flow Media). Bacteria living on these sheets convert ammonia in the wastewater to nitrates, a form of nitrogen that is non-toxic.
Secondary Clarification
The clarifiers slow the flow allowing heavy particles to settle to the bottom of the clarifier tank. The solids or sludge are pumped to the sludge thickener for further treatment.
Sand Filtration
The Mt. View Sanitary District utilizes a Dynasand ® filter system. The system removes solids from the secondary effluent achieving a clarity that allows downstream disinfection with ultraviolet light. The Dynasand ® filter is a continuous-backwash, upflow, deep-bed, granular-media filter system. The filter media is continuously cleaned by recycling the sand internally through an airlift pipe and sand washing. The cleansed sand is redistributed on top of the sand bed, allowing for a continuous, uninterrupted flow of filtrate and reject (backwash) water.
Ultraviolet Light Disinfection
Mt. View Sanitary District was the first POTW (Public Owned Treatment Works) operated in Northern California to use ultraviolet light for disinfection on a full-scale operation. MVSD has been able to eliminate the use of gaseous chlorine, sulphur dioxide and all Acutely Hazardous Materials (AHMs), which can be toxic to both humans and wildlife. The UV system uses the same ultraviolet light found in sunlight, but in a concentrated dose, to destroy harmful microorganisms present in the wastewater. The elimination of AHM’s from the plant premises has increased staff and public safety while decreasing District liability.
Outlet to the Marsh
The treated effluent flows into a series of marshes, rather than a deep-water outfall as most treated wastewater does. These marshes, enhanced by the reclaimed effluent, are rich and diverse in wildlife and easily accessible to students, birders, researchers, and the general public. To learn more about these wetlands, click here.
Sludge to Biosolids
Sludge Thickening
The Gravity Sludge Thickener is another settling tank that further separates solids from the liquid. The sludge from the bottom of the thickener is pumped to the Primary Digester. The overflow of water from the thickener is sent back to the influent wet well.
Sludge Digestion
Sludge solids are pumped into anaerobic digesters where bacteria, in an oxygen-free environment, break down solids, producing methane gas, carbon dioxide, and stabilized organic solids. The methane gas is used to fuel the plant boiler which maintains the desired temperature in the digester for the bacteria to thrive.
Sludge Dewatering
The Mt. View Sanitary District uses an Alfa Laval Sharples® Centrifuge. A centrifuge spins at a very high speed, forcing water and solids to separate. With this unit, we take sludge that is about 2% solids and remove water to increase it to approximately 20% to 25% solids. The water is returned to the influent wet well for treatment and the solids are sent to a landfill. The centrifuge enables us to achieve a high solids concentration, reducing hauling costs.
Biosolids
Solids from the centrifuge, which are called biosolids, are used as alternative daily cover at a landfill.