Parameter
Alternative 1: Compost expansion
Alternative 2: BH, AD, sludge drying
Total capital cost (inclusive of ITC reimbursement through IRA) Year 1: Total operation and maintenance (excluding labour)
$12,500,000
$50,707,000
$1,710,000
$1,580,000
Year 25: total operation and maintenance (excluding labour)
$1,843,000
$1,698,000
Year 1: Revenue from biogas sales, tipping fees, and RINs
-
$1,890,000
Year 1: Revenue from sale of Class A biosolid
$51,000 $51,000
$21,000
Total year 1 revenue
$1,911,000
Year 25: Revenue from biogas sales, Tipping fees, and RINs
-
$2,555,000
Year 25: Revenue from sale of Class A biosolid
$84,000 $84,000
$36,000
Total year 25 revenue
$2,591,000
Total capital and operating cost – Revenue for 25 yrs
$55,225,000
$35,407,000 $19,818,000
Savings over composting expansion (total) Saving over composting expansion (Annualised over 25 years)
-
$792,720
-
Source: RETTEW, September 2023 Financial Update Biosolids Upgrade Project
Table 1 Summary of 25-year economic evaluation
Boosting biogas recovery Since AD – by recovering biogas – offers a pathway to a financial return, any technology that can optimise the AD process should be considered as a potential strategic investment. This rationale underpins the adoption of biological hydrolysis (BH). Integrated immediately upstream of the AD system, BH technology is designed to condition sludge to accelerate the efficiency at which it can be digested, thus boosting biogas production. By removing the rate-limiting step (hydrolysis phase) from the digester, the 20-30-day hydraulic retention time (HRT) required for conventional mesophilic digestion is reduced to 15 days, significantly increasing the throughput of the digester. BH technology controls conditions in a multi- stage series of flow reactors to create an optimal environment for hydrolysis and acidification, promoting the development of volatile fatty acids to feed the digester. This allows the digestor to be dedicated to methanogenesis, effectively increasing its capacity. The
parameters of the BH flow reactors can also be adjusted to reduce the volume of produced biosolids while improving their quality to yield a pathogen-free biosolid. This higher quality biosolid product can be reused beneficially as a soil improver to help promote productive soils and stimulate plant growth. Critically, the BH + AD combination can achieve greater GHG emission reductions by realising 100% waste diversion from landfills. As a proven technology for pretreating sewage sludge prior to digestion, the BH process enables several benefits: reduced retention times in digesters, improved sludge digestibility, enhanced sludge stability to minimise foaming in the digestion plant, as well as increased volatile solids (VS) conversion in the digestion system. Additionally, BH is compliant with US EPA 40 CFR Part 503 regulations for Class A biosolids treatment. Making the economic case for BH and AD Traditionally, BH technology applications have been limited primarily to the UK. This is set to
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