Bio React AD boosts biogas, lowers NG use at 55-MGD WWTP

Overview

  • 32% increase in electricity from biogas between November 2018 and February 2019 (90-day period)
  • 10% decrease in natural gas use over the same period
  • 9% increase in Total Solids (TS) reduction
  •  $10,825 monthly cost savings in solids handling.
  • total gross monthly savings: $22,000

THE SITE

The 55-MGD wastewater treatment plant has been a leader in the use of renewable energy for wastewater treatment. It currently generates 95-percent of the energy it uses from onsite biogas, purchased natural gas, and solar energy generation. Only 5 percent of its energy requirement is imported from the local power utility.

PLANT OVERVIEW:
  • 14 primary and secondary anaerobic digesters make up the anaerobic digester complex. The primary digester contents are heated and maintained at about 95oF.
  • 1,000 KSCF (Kilo Standard Cubic Foot) of biogas are generated per day, with methane making up 60 percent of its content. 90 percent of the power used by the facility is generated onsite from biogas and natural gas.
  • 59,000 pounds of solids are destroyed each day on average in the process, for a biogas yield of approximately 11.3 SCF per pound of Total Solids.
  • Average TS and VS destruction in the digesters prior to the addition of the Drylet was 43% and 55% respectively.
BioReact AD application is simply added to daily biodigester maintenance operations.

THE PROCESS

BioReact AD was added to the digesters starting in November 2018 with a daily dosing of 50 lbs. The goal was to boost biogas and enhance solids reduction. The demonstration took place over 90 days. Training was provided to facility personnel on the best points of product application.

DEMONSTRATION PROTOCOL

Drylet proposed the addition of BioReact AD to the primary and secondary digesters to enable up to a 20-30% boost in solids destruction and biogas generation. Its engineers worked with the plantʼs personnel to develop a comprehensive demonstration protocol to guide the demonstration. Data was collected on a broad range of operational parameters such as biogas generation, biogas composition, alkalinity, sludge-haulage volumes, solids flows to and from the digesters, energy generation from various sources and natural gas costs.

BioReact AD was fed to both the 10 primary and 3 secondary digesters in varying amounts, totalling 50 Ibs per day (one of the secondary digesters was offline and under maintenance during the demonstration period.) The sludge-feeding arrangement into the secondary digesters is as follows:

Primary solids and thickened WAS are mixed in a sludge blending tank prior to being fed into the primary digesters. During the feeding of solids into the 10 primary digesters, the overflow of the corresponding quantity of fed raw digester solids (primary digestate) flows into the connected secondary digester. A single feed point was used for all the primary digesters. The overflow from three selected primary digesters (PD3, PD5, PD11), was used for applying product dosage into the secondary digesters.

OUTCOME

Within 90 days, results showed 32% boost to biogas generation led to a 10% decrease in natural gas use + $10,825 monthly cost savings in solids handling.
Total gross monthly savings: $22,000