Comments

David Shulman Tue, 09/10/19 - 22:27 I’ve cited below the new language proposed by the NYC DEP for sizing a GGI: “Therefore, for gravity grease interceptors, a means of converting the existing requirements into a minimum storage capacity in gallons has been inserted; i.e. the minimum required flow rate shall be multiplied by 3. The resulting number shall represent the minimum storage capacity in gallons if a gravity grease interceptor is installed.” This method for determining the minimum storage capacity of a GGI is highly unusual and, if used in real world applications, would likely lead to massive discharges FOG into NYC’s sanitary sewer system. GGI's sized according to this methodology would be grossly undersized and would not retain enough FOG to meet the preferred industry standard of 150 mg/L of discharged effluent. There exist no national performance standards or certifications for GGI's and therefore there is no data to indicate that these units effectively prevent FOG from entering the sanitary sewer. Beyond simply the uncertainty of a GGI’s effectiveness, the sizing method for GGI’s specified above by the NYC DEP does not in any way reflect the industry standards for GGI’s nor the science behind their operation. The primary means by which a GGI separates FOG from wastewater is through retention time and the difference in specific gravity between water and FOG. It’s for this reason the 2015 International Plumbing Code introduced a new section (1003.3.6) governing requirements for GGIs. The sizing requirement simply states “shall be determined by multiplying the peak drain flow into the interceptor in gallons per minute by a retention time of 30 minutes.” The IPC found that 30 minutes was the minimum required retention time to achieve significant separation in a GGI – this is ten times greater than the NYC DEP’s method of sizing would allow for. In contrast, HGI’s are sized by dividing the maximum peak flow of all fixtures attached to the unit over a given drainage period. An HGI or AGRD that has been certified by either the PDI-G101 or ASME A112.14.3 national performance standard has demonstrated in a 3rd party testing facility the ability to achieve at least a 90% separation efficiency up to a rated grease capacity of at least two lbs per every one gpm in flow rate with several manufacturers electing to determine the maximum grease capacity by continuing to add grease until the unit fails (when the efficiency drops below 90%). Any certified HGI or AGRD units have known efficiencies and grease capacity values which gives certainty to the jurisdiction and end user that the units will operate effectively. HGI’s and AGRD’s operate using a different technology than their GGI counterpart – in addition to using the difference in specific gravity between water and FOG, these types of units utilize a controlled flow of the incoming wastewater which increases efficiency and drastically decreases the necessary retention time.

David Shulman Tue, 09/10/19 - 22:28 Quoted below is one of the newly proposed changes by the NYC DEP regarding cleanout frequency for grease interceptors and automatic grease removal devices: "Add the 25% rule for maintenance of grease interceptors and automatic grease removal devices. The rule requires that all the fat, oil, grease, and solids be removed before 25% of the interceptor or device’s total liquid depth is exceeded. The 25% rule is an industry standard and is used by many municipalities across the country." This passage is not entirely correct – the 25% rule is an industry standard specifically for gravity grease interceptors. The 25% rule states that when 25% of the total liquid volume consists or FOG and/or solid debris, the unit has reached its maximum grease capacity and must be serviced. This rule has become the industry standard for gravity grease interceptors since no data exists to determine how much FOG these units may hold while still meeting industry performance standards. There is no reason for which the 25% rule should be applied to hydromechanical grease interceptors or automatic grease removal devices. Any HGI or AGRD unit that is certified to either the PDI-G101 or ASME A112.14.3 national performance standard has a known minimum rated capacity. Beyond that, several manufacturers have elected to go beyond that minimum requirement and test their units to absolute failure based on the testing standard. Using 3rd party tested data, these manufacturers who tested their units to failure have a known maximum rated grease capacity. The NYC DEP is absolutely correct in stating that HGI’s and AGRD’s should be sized based on the volume of liquid from the connected fixtures over a given drainage period. However, engineers and FSE operators should be able to calculate their required maintenance frequency using the maximum rated grease capacity provided by the manufacturer with accompanying testing data. Requiring FSE operators to maintain their units on an unnecessarily lower maintenance frequency both increases operating costs for the business owner and puts the more efficiently designed HGI and AGRD manufacturers at a competitive disadvantage. Many manufacturers, including Endura, have published online calculator tools to help end users, specifiers and AHJ's determine expected maintenance frequency requirements to aid in ongoing service as well as initial sizing e of HGI applications. Sizing and maintenance interval requirements using certified maximum rated grease capacity values are endorsed and explained in the ASME PEDH (Plumbing Engineering Design Handbook) 2016 – Volume 4 Chapter 8.