Regenesis - Resources - faq - Software Related

1. What do the additional demand factors mean on the ORC software spreadsheet?
The additional demand factors in the Summary of Estimated ORC Requirements table on the ORC spreadsheet are safety factors that account for uncertainty about potential sinks for oxygen. These factors are used to increase the ORC dose by the specified multiplier and provide contingency to account for the many uncertainties inherent in subsurface investigations and in-situ remediation projects. Potential sources of unexpected ORC demand include higher than expected contaminant mass (in the form of residual phase NAPL present as hot spots), natural organic matter, or reduced inorganic species, such as ferrous iron, manganese, or sulfides.

Additional oxygen demand factors are given for four categories:

Individual species like BTEX components, MTBE, reduced inorganics, etc.
Total Petroleum Hydrocarbons (TPH)
Biological Oxygen Demand (BOD)
Chemical Oxygen Demand (COD)

The user chooses the category on which to base the ORC design cost using the radio buttons in the table. The demand factors for each category are based on the degree to which each category provides a reasonable estimate of oxygen demand. For example, individual species like BTEX, MTBE, reduced inorganics, etc. (Category 1) are the most specific, least conservative measurement of oxygen demand, and COD (Category 4) is the most general, most conservative measurement of oxygen demand. The default additional demand factors for the each category are given in the following table. Although the default values summarized here have led to the design of many successful ORC applications, they can be modified based on the user's knowledge of the site characteristics and contaminant measurements.

Summary of Additional Demand Factors for the ORC Spreadsheet

Category	Additional Demand Factor	Comments
Individual species like BTEX components, MTBE, reduced inorganics, etc.	5	Measurements of individual species or sets of species will often underestimate the oxygen demand to a significant degree, so this category is given a high additional demand factor.
Total Petroleum Hydrocarbons (TPH)	2	TPH is given an additional demand factor of 2, because TPH is a more thorough measurement that will account for the background hydrocarbon contamination not considered in the individual species measurements. However, TPH does not include chemical reactions that consume oxygen (such as the oxidation of ferrous iron), so a safety factor must be used.
Biological Oxygen Demand (BOD)	2	BOD accounts for oxygen demand that is available to microorganisms and does not account for chemical reactions that consume oxygen. Thus, BOD is assigned a demand factor of 2.
Chemical Oxygen Demand (COD)	1	COD accounts for chemical and biological oxygen demand and is assigned a demand factor of 1 because it typically over represents the oxygen demand placed on ORC.

2. What do the additional demand factor and microbial demand factor mean in the HRC software spreadsheet?
The inclusion of a safety factor/additional demand factor is a typical engineering design technique used to provide a conservative estimate for the amount of HRC necessary for subsurface systems that have a high degree of variability and are minimally sampled for chemical/hydrological parameters. The safety factor/additional demand factor provides contingency to account for the many uncertainties inherent in subsurface investigations and in situ remediation projects. Potential sources of unexpected or contingent HRC demand include higher than expected contaminant mass (in the form of residual phase NAPL present of hot spots) and uncertainty about the quantity of HRC required for the reduction of manganese, iron, or sulfate.

The microbial demand factor accounts for non-targeted microbial demand for lactic acid and H₂ for processes that are not directly involved with either reduction of the chemical species included in the software (iron, sulfate, etc.) or in reductive dechlorination of VOCs. It includes microbial inefficiencies associated with lactate and/or H₂ metabolism and lactate use to grow biomass.