The Orange County Sanitation District (OCSD), Huntington Beach, California provides wastewater collection, treatment, and disposal services for approximately 2.6 million people in central and northwest Orange County. OCSD operates two wastewater treatment plants in Huntington Beach, CA that process an average of 185 MGD (million gallons per day).

OCSD Plant #2, which came on stream in 2018, handles 65 MGD of the District’s wastewater stream. In the two-story Centrifuge Building, where sludge dewatering and odor removal take place, acoustic treatment was specified in order to reduce the excessively high sound level generated by a myriad of noise-producing equipment and comply with OSHA-designated guidelines. On the second floor, there are five Alfa-Laval G3 centrifuges, two to three of which are operated at any one time. The first floor features piston pumps, a plant air system with two 500-gallon air receiver tanks, exhaust fans, mechanical grinders, and a variety of other noisy pieces of equipment. 

 A health hazard

The two rooms have areas of 6,783 ft² (51 ft. wide x 133 ft. long), with the first floor having a ceiling height of 212 ft . The , and the second floor has a two-level ceiling — one section is 11 ft. high, and the other is 21 ft. high. with a height ranging from 24 ft. to 26 ft . Most of the walls and floors are concrete, although there is some drywall on the second floor. The first floorfirst-floor ceiling is concrete, while the second floorsecond-floor ceiling is corrugated steel on the high roof and concrete on the low roof. 

That combination of loud industrial equipment, cavernous space, and highly reflective surfaces creates an acoustic nightmare that is hazardous to the health of operating personnel and decreases productivity because of the difficulty of person-to-person communications. 

Brown & Caldwell (Walnut Creek, CA) created the specifications for the construction of the building. Included in the specs was the requirement that the ambient noise level in the plant be below 90 Db, and initially called for 50% of the wall and ceiling area to be treated with acoustic panels to try to meet that goal. Given the number of windows, the extent of the piping, the electrical utilities and the HVAC system, reaching that coverage goal was not possible. In the end, the acoustic noise reduction spec was achieved with panel coverage that worked out as follows: First floor walls — 36.6%; first floor ceiling—19.6%; second floor walls — 36.6%; and second floor ceilings — 53.1%.  

Layout and design

The layout of the panels in the building was done by Ryan Castle, Project Engineer with Shimmick Construction Co., Inc. (Huntington Beach, California). 

The final design called for a total of 702 perforated, v-ridged aluminum acoustic pEckel Functional Panels ranging in size from super-sized 48 in. x 120 in. panels down to 18 in. x 36 in. panels fabricated to fit in between wall obstacles. 149 panels were installed on the second-floor ceiling and 211 on the second-floor walls. On the first floor, 133 panels were installed on the ceilings, 95 on the walls, and 114 on the support columns. The panels were painted standard white.    

The plant was started up and went operational before the panels were installed, so an anecdotal comparison could be made between the ambient noise level in the two rooms before and after panel installation. 

According to Ryan Castle, “Before the panels were installed the plant was very loud and full of mechanical and operational echoes. All the moving parts and machinery could be heard everywhere as the sound just bounced back and forth off of all the empty space. The panels were then installed within the empty spaces on the walls, the columns, over some piping and conduit, on the ceilings, and around the HVAC systems. The panels helped trap the sound from reverberating off the empty spaces and the overall noise reduction was instantly noticeable.”