Anaerobic Digester Tender: Specifications And Evaluation Criteria

An anaerobic digester tender is the procurement document that turns a biogas project into comparable, awardable bids. The tender fails when it specifies only a volume and a price, because suppliers then fill the gaps with their own assumptions and the lowest bid is the least complete. A good tender pins down the feedstock, retention time, operating temperature, gas pressure, coating zones and the responsibility split, then evaluates on lifecycle and compliance, not just capital cost. Center Enamel responds to digester tenders with scoped bolted-tank packages and the certificates tenders require.

The tender should name the feedstock and its total solids, the retention time, the temperature band, the biogas pressure and the coating zones, plus who designs the foundation, erects the tank and commissions it. It should also state the acceptance test - typically a 1,500 V holiday-spark test on every panel and a hydrostatic or gas-tightness check. Without these, evaluators cannot compare bids on equal terms.

• Feedstock and total solids (8-12% for CSTR).
• Retention time and temperature band (35-38 C).
• Biogas pressure and roof class (5-30 mbar).
• Coating zones and acceptance test defined.

Evaluate on scope completeness first, then technical compliance, then lifecycle cost. Score whether the bid includes the gas-tight roof, nozzles, mixer interface and erection, whether the coating class meets the zone specification, and whether the structural calculation is to AWWA D103 or ISO 28765. Only after scope and compliance match should price decide, and even then a 30-year coating life beats a cheap shell that fails the gas zone.

• Scope completeness: roof, nozzles, erection included?
• Technical compliance: coating class and codes met?
• Lifecycle: 30-year coating vs cheap single coat.
• Price last, after scope and compliance match.

Make anaerobic digester tender bids evaluable and stop suppliers hiding scope with these specification rows: retention of 20-40 days at 35-38 C, gas pressure of 5-30 mbar, coating class GFS 2C2F or FBE by zone, a 1,500 V 100% holiday-spark acceptance test, and a shell calculation to AWWA D103-19 and ISO 28765. Pinned into the document, they let evaluators score bids on completeness rather than capital price.

A 2019 biogas engineering project in Cangzhou, China, used two Glass-Fused-to-Steel bolted tanks totalling 3,077 m3. As a procured biogas delivery it demonstrates a project awarded and built to a specified scope for biogas duty. Diameter and height are not recorded in the verified project data and are reported Not Provided.

Most anaerobic digester tenders fail on a few repeated gaps. The coating is specified by a generic name rather than by zone and pH class. The gasholder is omitted because it is assumed part of the digester. The acceptance test is left vague instead of a 1,500 V holiday-spark requirement. The erection and commissioning responsibility is undefined, so every bidder prices it differently. Closing these four gaps turns a price-only tender into an evaluable one, and the lowest bid stops being the least complete.

• Coating named without zone or pH class.
• Gasholder assumed part of the digester.
• Acceptance test left vague, not 1,500 V specified.
• Erection and commissioning responsibility undefined.
• Closing gaps makes bids comparable on scope.

Center Enamel responds to anaerobic digester tenders with scoped bolted-tank packages and the certificates tenders require: ISO 9001, ISO 45001, NSF/ANSI 61, EN 1090 (CE), ISO 28765 and WRAS approvals, a shell calculation to AWWA D103-19 and ISO 28765, and a 100% 1,500 V holiday-spark test on every panel. The company has produced GFS tanks since 2008 and delivered more than 30,000 projects across 100+ countries.

• Bid-ready certificate pack and calculation.
• Per-zone coating specification for tender compliance.
• Method statement and erection support.
• Standard ex-works lead time about 30 days (1,000-10,000 m3).

Feedstock and total solids, retention time, operating temperature band, biogas pressure, coating zones, and the responsibility split for foundation, erection and commissioning, plus the acceptance test such as a 1,500 V holiday-spark test.

On scope completeness first, then technical compliance, then lifecycle cost, with price last. Score whether the roof, nozzles, mixer interface and erection are included and whether the coating class meets the zone specification.

Because suppliers fill the gaps with their own assumptions, so the lowest bid omits the roof or the erection. The tender must pin down scope so bids are comparable, not just cheap.

A 100% surface 1,500 V holiday-spark test on every panel, with records, and a hydrostatic or gas-tightness check. It is the non-negotiable evidence of a gas-tight biogas digester.

Bolted tanks to AWWA D103-19 and ISO 28765; coatings to NSF/ANSI 61 or WRAS where potable contact applies; EN 1090 (CE) marking for Europe. Reference the certificate, not the claim.

Yes. Center Enamel supplies scoped bolted GFS, FBE, stainless-steel and carbon-steel digester packages with the certificate pack, shell calculation and acceptance-test records tenders require.

A CSTR runs 20-40 days at mesophilic 35-38 C, which sets the digester volume. The tender should fix these so all bidders size the tank identically.

A 2019 biogas engineering project in Cangzhou, China, used two GFS bolted tanks totalling 3,077 m3 - a build awarded and executed to a specified scope.

The digestate tank. It is separate from the digester and sized to season plus regulation, so the tender must scope it distinctly or the digester bid will be quietly unbalanced.

An anaerobic digester tender must specify feedstock, retention time, temperature, gas pressure, coating zones and the responsibility split, then evaluate bids on scope completeness, technical compliance and lifecycle cost - with price last - so the lowest bid is not the least complete. Require a 1,500 V holiday-spark acceptance test and keep digestate storage as a separate scope. A tender that closes the four common gaps - coating zone, gasholder, acceptance test and erection responsibility - is the one that produces comparable, awardable bids rather than a price race that hides scope. The evaluator who scores scope first and price last protects the project from the cheapest, least complete offer. Center Enamel responds to such tenders with scoped bolted packages and certificates, demonstrated by a 2019 Cangzhou biogas project of two tanks totalling 3,077 m3.