article waste water san diego

8/17/2019 Article Waste Water San Diego

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www.alfalaval.com/here here november 2003 11

A t first, Hollywood and wastewater treatment may seem like anunlikely pair. But the City of San Diego Metropolitan Waste-

water Department’s (MWWD) Metro Biosolids Center (MBC)

is an uncommon place.

From serving as a two-time movie set to winning awards for strik-

ing architectural design, the MBC has been recognized as an industry

leader in creative thinking, community involvement and environ-

mental responsibility.

The MWWD includes several facilities interconnected through an

elaborate pipeline system, including the MBC , the Point Loma Waste-

water Treatment Plant and the North City Water Reclamation Plant.

Completed in 1998, the MBC was designed with an artistic flair not

commonly associated with government departments. Older MWWD

buildings have been renovated to reflect a similar sensibility, inte-

grating the buildings intothe communities they serve.

A real powerhouseThe MWWD’s real strength

extends far beyond its facili-

ties’ good looks.

The MWWD serves a 450-

square-mile area in Greater

San Diego. Two million peo-

ple from 16 cities and districts generate up to 680,000 cubic metres

(180 million gallons) of wastewater daily. The plant handles this chal-

lenge with ease. In the process, it not only generates enough power to

be entirely self-sufficient, but excess power is sold to the local energy

Pictureperfect

Pretend you’re a movie scout,

looking for a unique and elegantlocation. After an extensive

search, you find it … at a waste-water treatment plant!

wastewatertreatment

TEXT JEAN WESLEY PHOTOS PHILIPP RITTERMAN


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www.alfalaval.com/here here november 2003 132 here november 2003 an international magazine from alfa laval

grid, offsetting operating costs and making a positive environmental

impact on the community.

Thickening and digesting The heart of the MWWD system,the MBC, processes both raw sludge from North City and digested

sludge from the Point Loma plant. The digested solids arrive via a 17-

mile pipeline.

This “offsite” solids treatment is f airly rare in the industry and re-

quired extensive planning. In fact, the MWWD invested over 33 mil-

lion U.S. dollars in engineering and construction management costs

for the MBC development.

Raw sludge is treated at both MBC and Point Loma using the same

process. After degritting and screening to eliminate large materials,

raw solids are directed to chambers to remove heavy inorganic parti-

cles and organic solids. Ferric chloride and organic polymers are

added to help the waste particles bond together and settle out.

At this point in the process, approximately 80 percent of the total

suspended solids in the water have been removed, and the treated

wastewater, or effluent, can be discharged to the ocean. The sludge

continues on for additional processing.

Alfa Laval spiral heat exchangers are used to preheat the sludge. In

any given minute, 2,500–3,000 litres (650–780 gal lons) of sludge flow

through the spirals.

The undigested sludge from the North City plant is pumped into

one of the MBC digesters. A heat and bacterial process similar tohuman digestion reduces the volume dramatically. Over 15 to 20

days, bacteria consume approximately 60 percent of organic matter,

reducing volatile solids and creating digested sludge in the process.

The spiral heat exchangers also maintain the heat in the airtight

digesters, keeping the sludge at the optimum temperature for diges-

tion. The spiral heat exchangers are easier to maintain, are more effi-

cient and have a smaller footprint than the shell-and-tube technology

commonly used in the past.

Reduced disposal costs After digestion, sludge from boththe Point Loma and North City facilities is commingled at the MBC

and it all moves on for processing in Alfa Laval decanter centrifuges.

These decanters dewater the blended wet biosolids by using centrifu -

gal force to remove water.

As the decanter rotates, the liquid, or centrate, is separated from

the dewatered biosolids. The centrate returns through the sewer sys-

tem to Point Loma for processing. The pumps feeding the decanters

In wastewater treatment, down-

time is unacceptable – equipment

downtime can quickly lead to harm-

ful environmental consequences. In

this environment, preventative main-tenance is key.

Preventing downtime led the Met-

ropolitan Wastewater Department to

choose a Performance Agreement

with Alfa Laval for equipment main-

tenance at the Metro Biosolids Cen-

ter.

The Alfa Laval Performance Agree-

ment pertains to eight DS-706 dewa-

tering decanters and five PM-95000

thickening decanters. (The Alfa Laval

spiral heat exchangers on-site are

not part of the agreement, as they

are virtually maintenance free.)

Routine equipment maintenance

and inspection at regular intervals;

minor, intermediate and major serv-

ice over the lifecycle of the equip-ment; labour and part expenses;

telephone technical support; onsite

training; and the extended warranty

are all rolled into one fixed cost.

This program allows accurate

budget planning and eliminates un-

pleasant financial surprises if a tech-

nical need arises.

In between visits, the MBC’s inter-

nal staff completes regular mainte-

nance. They have ongoing access to

technical resources at Alfa Laval’s

Contact Center via phone. Plus, on-

site training for new staff ensures

that the staff is trained in all proper

maintenance procedures.

This Performance Agreement has

been in effect since 2001 and isscheduled to run until 2005, with a

renewal at the end of each 12-month

period.

Jack Swerlein, Plant Superinten-

dent at the MWWD, says: “We have

saved 1.8 million dollars on our an-

nual biosolid disposal costs after

changing our dewatering process

from a belt press operation to Alfa

Laval centrifuges. The Performance

Agreement and Extended Warranty

have played a key role in achieving

these cost savings".

The MWWD serves a450-square-mile areain Greater San Diego.

The MBC was designed with anartistic flair not commonly associatedwith government departments.

Flowing smoothly

Jack Swerlein, Plant Superintendent

at the MWWD.

33www.alfalaval.com/here/sludge/sandiego


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14 here november 2003 an international magazine from alfa laval

automatically adjust the speed, depending on programmed parame-

ters and the number of centrifuges on line.

The remaining biosolids, or cake, are the consistency of wet clay,which is transported to nearby landfills or land applied for beneficial

use. The decanters help produce a high quality cake; MBC reduced its

annual disposal costs by 1.8 million dollars thanks to the improved

cake quality produced by the decanters.

The power of self-sufficiency The digestion process andliquid biosolids storage tanks both create methane gas as a byproduct.

This is captured to produce electricity to meet

the facilities’ power needs, and the excess pow-

ers other homes in the community. The MBC

saves the city approximately 45,000 U.S. dol-

lars a week by generating its own power. Even

when the city of San Diego was entangled in

an energy crisis in 2002, all MWWD facilities

remained operational during brownouts.For all of its environmental efforts, the

MWWD was the first publicly owned waste-

water treatment operation in the USA to

receive ISO 14001 Certification from the Inter-

national Organization for Standardization in

Geneva, Switzerland. This award is a testament

to the department’s unwavering respect for the

environment.

Up and running With the combination of quality equipment, self-sufficient power, strong internal resources

and an ongoing Performance Agreement with Alfa Laval (see sidebar),

downtime is minimized or often eliminated – allowing the system tomeet the stringent standards of the Environmental Protection

Agency (EPA ).

While internal maintenance personnel do most of the daily main-

tenance, the Alfa Laval Performance Agreement provides routine

equipment maintenance, technical support and onsite training.

The result: a system as dependable as it is striking – one that’s pic-

ture perfect.

Extruded sticks (briquettes) of sludge, covered with gold and mounted on a concrete wall.

The decanter centrifuges dewater the blended wet biosolids.

The spiral heat exchangers are

used to preheat the sludge and to

keep it at the optimum tempera-

ture for digestion.

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