Notice to: Industrial Users discharge of Tetramethylammonium Hydroxide (TMAH)
The Central Regional Wastewater System (CRWS) Treatment Plant (Plant) began experiencing larger than normal chlorine demand as part of its disinfection process at the beginning of January 2018. The Authority (Trinity River Authority) immediately commenced a forensic investigation with the assistance of professional consultants to determine the cause of the increased chlorine demand. A major cause of the chlorine demand increase has been traced to higher than expected levels of Tetramethylammonium Hydroxide (TMAH) that has accumulated and inhabited the Plants biomass. At least one source of significant TMAH discharge has been traced to a centralized waste treatment facility in close proximity to the Plant. Additional sampling efforts have identified that TMAH is also being delivered to the Plant by all of the combined interceptor systems serving the contracting parties.
Deliveries of TMAH to the Plant have resulted in a condition known as “nitrite lock”. In this condition, nitrite is not oxidized to nitrate and nitrite passes through the treatment process to the chlorine contact basin. One milligram per liter (mg/l) of nitrite can consume approximately 5 mg/l of chlorine. Chlorine is used for disinfection at the Plant and typically requires a dosing rate between 4- 7mg/l. The nitrite provides an additional demand on top of the disinfection demand. This combined demand (disinfection plus nitrite) has required the Authority to dose chlorine at a rate that is two to four times higher than typically required to achieve permit disinfection requirements. The additional cost associated with required chlorine usage, additional testing and staff time total $563,840.00, as of May 31, 2018.
To date, the condition affecting the CRWS Plant has not resulted in a violation of the discharge limits or other requirements of the Authority’s Texas Pollutant Discharge Elimination System permit.
Discharge of TMAH Immediately Prohibited
The Authority has begun the process of modifying its pretreatment program to specifically prohibit the discharge of measurable quantities of TMAH and other inhibitory compounds to the CRWS Plant. Pursuant to the contracts for treatment services between CRWS customers and the Authority, customers shall not discharge any substance that creates conditions “deleterious to structures or treatment process,” or which require “unusual provisions, alteration, or expense to handle such substances[s].” Article IV, Section 4.03. In addition, CRWS customer contracts with the Authority prohibit the discharge of any substance “in sufficient quantity to injure or interfere with any wastewater treatment process.” Article IV, Section 4.03.
The Authority has identified that TMAH constitutes such a substance. Accordingly, the discharge of measurable quantities of TMAH for treatment at the CRWS Plant are immediately prohibited.
In conferring with researchers and engineering consultants, the Authority has determined that, in order to recover from nitrite lock, the above-described prohibition is necessary. Recovery may require twenty weeks or more, dependent upon the immediate elimination of TMAH discharge to the CRWS system. As the additional treatment expenses that will be passed on to CRWS customers are substantial, it is in the customers best interest to take immediate action to cease TMAH discharge by industrial users within our jurisdictions.