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The Infrastructure Subcommittee focused on developing a "Special Waste" conveyance plumbing maintenance Guidebook intended to help those institutions experiencing problems with mercury contaminated biomass within their systems. Research from several institutions provided information indicating that the organic materials entering these systems act as a food source for biological growth. This "biomass" was found to readily absorb or accumulate mercury within these "Special Waste" plumbing systems. Beth Israel Hospital, for example, determined that the biomass inside their conveyance system contained as much as 1,000 parts per million (ppm) of mercury. As bits of these biosolids would periodically break off and be flushed out of the systems, they would carry the concentrated mercury with them. This would result in a display of elevated concentrations of mercury, once the solids were digested and the sample analyzed. Some of the maintenance procedures that are discussed in this Guidebook for the control or elimination of biomass growth are: trap cleaning, powerwashing, chemical cleaning and associated procedures.
As previously explained, mercury accumulation within "Special Waste" conveyance piping systems containing biomass growth with mercury creates a complicated wastewater compliance issue. But, through institutional efforts, two techniques, trap cleaning and conveyance pipe powerwashing, have been identified, tested and proven to be very successful with biomass removal and mercury sources identification.
The trap cleaning procedures simply require that a trap be removed, the contents be collected for off-site disposal, and the trap cleaned with a rag or brush prior to being placed back into operation. The powerwashing procedure provides a physical scouring effect on the accumulated biomass adhered to plumbing and piping infrastructure. Powerwashing is an effective, but not permanent, method for removing biomass and preventing biosolids from appearing in the effluent discharges. Powerwashing techniques are most efficient when performed on glass piping. With thermoplastic piping, some technique modification is required. Powerwashing activities usually require a minimum of two people: One serving as the powerwash operator; and the other as an observer of the nozzle and hose as it moves through the conveyance piping.
Since trap cleaning and conveyance pipe powerwashing will not permanently remove biomass, periodic cleanings will be necessary to help ensure recurring growth is removed. In an effort to augment or perhaps even eliminate the need for trap cleaning and powerwashing activities, several means of chemical cleaning were also tested and evaluated. Some of the chemicals succeeded in softening or loosening the biomass, and others actually facilitated the removal of bulky segments of biomass. But not one of the methods tested was capable of completely removing biomass from the piping systems. In addition, some of the chemicals had significant health and safety issues associated with them, making their use in the field impractical. Consequently, not one of the chemical cleaning means tested is recommended for use.
The Infrastructure Subcommittee also found that neutralization sumps or tanks (chip tanks) that are often used for the pretreatment of wastewaters containing dilute acids and alkalis from laboratory sinks cannot be used in facilities discharging significant quantities of organic materials due to the fact that the biomass present will coat the marble chips, rendering the media useless. It is, therefore, recommended that institutions review the efficacy of these systems, and replace them with active (adjustable) neutralization systems when and where appropriate.
Adjustment tanks for pH can be used to treat all "Special Wastes" including dilute acids and alkalis, and wastewater containing organic materials. The anticipated flows through the waste piping system may dictate the use of a two tank system; the first tank being a mix tank for rough neutralizing and a trim tank for final adjustment prior to discharge to the sewer system. As required by the Massachusetts State Plumbing Code, 248 CMR 2.13 (12/1/93), all plans and specifications for "Special Waste" piping and pretreatment systems shall be prepared by a Registered Professional Engineer and shall be submitted to the local Plumbing Inspector for approval prior to installation. Systems adjusting pH are to be accessible for maintenance, repair, operation, and sampling procedures. The operation and maintenance requirements of these pH adjustment systems are detailed in 314 CMR 12.00, Division of Water Pollution Control regulations. In addition, these wastewater pretreatment systems are required to be operated by certified operators. Certification requirements for wastewater pretreatment system operators are detailed in 257 CMR 2.00, Board of Certification of Wastewater Treatment Facilities regulations.
The installation of flow monitoring devices at several facilities (carried out as part of the Infrastructure Subcommittee's analysis of wastewater characteristics) also provided documentation of the tendency to over estimate institutional flow rates. Since the MWRA bases permitting and sampling fees, in part, on flow, additional sampling and permitting fees may be avoided if actual flow rates are obtained via the installation of flow monitoring devices. In most cases, these devices can pay for themselves in a short period of time from savings derived from reduced sampling and reporting requirements.
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