MHMUA's Wastewater Treatment Processes
Screening and Grit Removal - Debris and heavy inorganic solids (sand, gravel, etc.) are removed from the flow that could damage subsequent process equipment.
Flow Equalization - A 1.5 million gallon Equalization Tank (Surge Tank No. 1) attenuates flow and concentration peaks to achieve a relatively constant flowrate and loading to downstream treatment plant processes.
Primary Settling Tanks - Removes heavy organic solids and the settled solids from the Intermediate Settling Tanks through the use of 8 Primary Settling Tanks, distributed between Plants No. 1 (4 tanks), No. 2 (2 tanks), and No. 3 (2 tanks). The solids removed from these tanks are directed to the Sludge Mixing & Storage Tank.
Trickling Filters and Intermediate Settling Tanks - The three trickling filters (two in Plant No. 1 and one in Plant No. 2) provide reliable, inexpensive removal of biodegradable organics from the primary effluent of Plants No. 1 and No. 2. The settled solids from the four Intermediate Settling Tanks (two in both Plant No. 1 and No. 2) are directed back to the head of the plant for removal in the Primary Settling Tanks.
Powdered Activated Carbon/Activated Sludge (PAC/AS - This variation of the Activated Sludge process removes ammonia, biodegradable organics, and non-biodegradable organic compounds (including priority pollutants) through biological oxidation and absorption/adsorption onto the powdered carbon.
Secondary Settling Tanks - Two tanks in Plant No. 3 provide for the separation of the settled PAC/AS from the clarified secondary effluent. The Return Activated Sludge is directed to the Scrubbing Mixing Chamber where it is mixed with virgin carbon, regenerated carbon and the liquid phase discharge from the Wet Air Regeneration (WAR) reactor, sludge dryer off-gases, and the primary effluent from Plant No. 3, prior to being returned back to the PAC/AS system. The Waste Activated Sludge is directed to the WAR reactor.
High-Rate Rapid Sand Filtration - The four filter cells provide for the tertiary removal of suspended solids in the effluent from the Secondary Settling Tanks. The backwash from these filter cells is directed back to the head of the plant for additional treatment.
Disinfection - The filtered effluent is disinfected with Sodium Hypochlorite in Chlorine Contact Tanks, and the residual chlorine is then removed by Sodium Bisulfite addition.
Post Aeration - The dissolved oxygen content in the treated effluent is increased prior to discharge into the North Branch of the Rancocas Creek, through the use of two Post Aeration Tanks equipped with surface aerators followed by Cascade Aeration.
MHMUA's Biosolids Treatment Processes
Wet Air Regeneration (WAR) - The Waste Activated Sludge from the PAC/AS system is directed to the WAR reactor, where the organics are oxidized under high pressure (900-1000 psig) and high temperature (450 - 500 degrees F) to carbon dioxide, water, regenerated powdered carbon, ash, and soluble short chain organic acids. The liquid phase discharge from the WAR reactor (including the regenerated powdered carbon) is directed to the Scrubbing Mixing Chamber where it is mixed with the Return Activated Sludge, virgin carbon, sludge dryer off-gases, and the primary effluent from Plant No. 3, prior to being returned back to the activated sludge system for additional treatment.
Sludge Mixing & Storage Tank - A 350,000 gallon sludge storage tank is used to store and blend the settled solids from the Primary Settling Tanks with other external miscellaneous trucked-in biosolids, prior to biosolids processing.
Thickening - Biosolids from the Sludge Mixing & Storage Tank are directed to a Rotary Drum Thickener, which removes water and increases the solids content to approximately 4 - 6% Total Solids (TS) prior to Belt Filter Press dewatering. The filtrate from this process is recycled back to the head of the plant for additional treatment.
Dewatering - Biosolids from the Rotary Drum Thickener are directed to a 125,000 gallon Thickened Sludge Storage Tank, which stores the thickened sludge prior to dewatering with Belt Filter Presses. The Belt Filter Presses dewaters the biosolids to a solids content of approximately 25% - 30% TS. The combination of filtrate and washwater from this process is recycled back to Surge Tank No. 1 for additional treatment.
Drying - The final biosolids treatment process is the indirect drying of the biosolids to a solids content of approximately 90 - 99% TS through the use of a dehydration unit (dryer). The dryer is a horizontal unit with hollow (hot oil filled) flights on a rotating auger (which conveys the sludge through the dryer) within a counter-rotating tube (which is externally heated by gas burners). The steam and off-gases from the dryer are passed through an Odor Control System to remove the volatile organics and particulate matter.
Disposal - The bulk of the dewatered biosolids that are not dried are composted at the Burlington County Resource Recovery Complex, and lesser quantities are incinerated at the Stony Brook Regional Sewerage Authority and at the Atlantic County Utilities Authority. The dewatered biosolids that are dried are disposed at G.R.O.W.S. Landfill, Morrisville, PA.