In 2015, the City of Sioux Falls (the “City”) “commissioned the Sioux Falls Water Reclamation Facility Digester Gas Conditioning System Project (the ‘Project’) to add a new digester gas conditioning system to its water reclamation facility that would remove high concentrations of hydrogen sulfide to concentrations below 100 parts per million volume (ppmv), and that would remove siloxane to concentrations below 100 parts per billion by volume (ppbv), which would then enable the City to operate its GE Jenbacher gas engine generator to create electricity for the benefit of the City.”

For reasons which are disputed by the various parties in this matter, the Project, particularly the Azzuro system meant to remove hydrogen sulfide, was unsuccessful.

The City brought this litigation seeking damages against some parties involved with the Project. One of those Defendants, Azzuro, Inc., brought a counterclaim against the City.

The City disclosed Lowell Howard, PE, as a retained expert witness in this matter. Azzuro filed a motion to exclude in part the testimony of Howard.

Biogas Expert Witness

Lowell E. Howard, PE has 40 years of experience designing, manufacturing, and installing or supplying biogas treatment systems. He has been involved in 20-40 biogas treatment system projects around the world, including several where the primary goal of the project was to remove hydrogen sulfide from biogas.

Get the full story on challenges to Lowell Howard’s expert opinions and testimony with an in-depth Challenge Study.

Discussion by the Court

Azzuro challenged Howard’s opinions “because he is not qualified as an expert by knowledge, experience, training, or education on issues relating to biological desulfurization systems as required by Rule 702.”

Azzuro argued that Howard’s testimony demonstrates an unawareness that renders any opinion he may have about a required oxygen level to be a “fundamentally unsupported conclusion based on pure speculation.”

The City argued that Howard used “his experience and educated understanding of basic biological and chemistry principles and chemical processes at play in the biogas treatment industry, as well as the engineering principles and chemical processes necessary to remove hydrogen sulfide from biogas, to explain why the Azzuro system did not and could not work as designed.” And the City argued that although Azzuro “contended that biological systems are vastly different from media-based systems, it does not cite to any competing expert’s opinion, legal authority, or fact in the record to support that conclusory statement.”

The City argued that although Howard “has not previously worked on a biological system like the Azzuro system, Howard has certainly demonstrated a sufficient understanding of the biogas industry as a whole, the design of biogas systems, and engineering principles and the chemical processes that must be considered in a biological hydrogen sulfide removal system in order to meet the qualification threshold under Rule 702 and Daubert.”

Analysis

The Court is persuaded by the City’s arguments. The Court believed that this is also the case with respect to Azzuro’s argument that Howard’s opinions lack a proper factual foundation. While Howard made the statements quoted above about his unfamiliarity with the Azzuro system, those statements are not automatically fatal to admissibility when the full record is considered. Howard’s report and further testimony suggested that he studied the Azzuro system and that, based upon this review, he does not believe it would work.

Held

The Court denied Azzuro, Inc.’s motion to exclude in part the testimony of Lowell E. Howard.

Key Takeaway

Howard is a decades-long veteran of the biogas industry. Where he opines on oxygen requirements for hydrogen sulfide removal, he does so relying on concepts of “[b]asic chemistry.” Howard does not hold himself out as an expert on the particular growth media in the Azzuro system or biological solutions in general. Rather, he admits some unfamiliarity with those systems and how they operate except in the broadest sense. Howard supplemented his knowledge by reading a study about biological systems, but he did not start on a clean slate because there are not different periodic tables of elements for fixed-bed media systems and biological systems.

Case Details:

Case Caption:	City Of Sioux Falls V. Azzuro, Inc.
Docket Number:	4:22cv4052
Court Name:	United States District Court, South Dakota
Order Date:	March 25, 2026

Category: Biogas Expert Witness

Biogas Expert Allowed to Opine on Oxygen Requirements

Biogas Expert Allowed to Opine on Oxygen Requirements