13.5 Industrial Water Drainage & Waste Pretreatment

Industrial Water Drainage & Waste Pretreatment

Content Area A of the Florida blueprint is Drainage at 20 percent, and its sixth named sub-topic is industrial water drainage systems, with the content outline calling for knowledge of system sizing and design, materials, code requirements, terms and definitions, and "proper treating of industrial waste." This section closes that gap.

The central idea is simple: the sanitary drainage system is designed for domestic sewage at room temperature and neutral pH. Anything that arrives hotter, more corrosive, more concentrated or more voluminous than that has to be conditioned before it is allowed in.

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1. Classifying the Stream

Florida's plumbing code sorts industrial discharges by what they are, not by what industry produced them:

[!IMPORTANT] FPC Section 702.5, Temperature Rating, is the sentence the blueprint's industrial water drainage sub-topic actually turns on: "Where the waste water temperature will be greater than 140 degrees F (60 degrees C), the sanitary drainage piping material shall be rated for the highest temperature of the waste water." Standard DWV PVC softens and distorts well below the temperature of boiler blowdown or a commercial sterilizer discharge. The design answer is either to cool the stream before it enters the drain or to install piping rated for the temperature — cast iron, high-temperature CPVC, polypropylene or stainless — for the affected run.

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2. The Four Industrial Streams You Will Actually Meet

Cooling Water and Condenser Discharge

Once-through cooling water from an air conditioning plant, a process chiller or a refrigeration condenser is nonpotable clear-water waste. It carries no solids and little chemistry, but it arrives warm and in volume. It discharges indirectly through an air break or an air gap into a trapped and vented receptor under FPC Section 802.1.5. Where the discharge is continuous or semicontinuous into a storm drainage system, FPC Chapter 11 equates each gallon per minute of such discharge to 96 square feet of roof area at a 1 inch per hour rainfall rate for sizing purposes — a useful conversion when a chiller condensate line is tied into a storm main.

Boiler Blowdown

Boiler blowdown is the worst-case combination: high temperature, high alkalinity, high dissolved solids and high pressure. It is not simply piped to a floor sink. The standard arrangement is:

1. Blowdown separator (flash tank) — drops the blowdown to atmospheric pressure and vents the flash steam safely outdoors.
2. Aftercooler — tempers the remaining liquid by blending cold makeup water, usually to a local sewer-use limit commonly set around 140 degrees F.
3. Indirect discharge to a trapped, vented receptor through an air break or air gap as nonpotable clear-water waste.
4. Piping rated for temperature on the hot side of the aftercooler under FPC 702.5.

Process Rinse and Wash Water

Plating lines, printing operations, photo processing, metal finishing and food processing produce rinse water carrying metals, solvents, dyes or organics. This stream is controlled almost entirely by the local sewer-use / industrial pretreatment ordinance issued by the utility under its federal pretreatment program. The plumbing contractor's obligations are to keep the industrial stream segregated from domestic sewage until it has been treated, to provide the sampling access the utility requires, and to use piping compatible with the chemistry.

Chemical and Acid Waste

Laboratory, battery-room and process acid waste is the one stream the plumbing code addresses directly and severely:

• FPC Section 702.6 requires a chemical waste system to be completely separated from the sanitary drainage system, treated per Section 803.2 before discharging into it, and built of material resistant to corrosion and degradation for the concentrations of chemicals involved.
• FPC Section 803.1 prohibits discharging corrosive liquids, spent acids or other harmful chemicals that would destroy or injure a drain, sewer, soil or waste pipe, create noxious or toxic fumes, or interfere with sewage treatment processes, without being thoroughly diluted, neutralized or treated by passing through an approved dilution or neutralizing device. That device must be automatically provided with a sufficient supply of diluting water or neutralizing medium, and the nature of the waste and the method of its treatment must be approved prior to installation.
• FPC Section 803.2 requires chemical drainage and vent systems to be designed and installed to the code, completely separated from the sanitary systems, with no discharge to sanitary until treated under 803.1.

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3. The Pretreatment Train

An industrial discharge is conditioned in a predictable order, and understanding the order is what the blueprint means by "proper treating of industrial waste":

1. Screening and settling. Coarse solids and grit are removed first so they do not foul everything downstream. FPC Section 1003.5 requires sand and heavy-solids interceptors to be designed and located with ready access for cleaning and to have a water seal of not less than 6 inches.
2. Separation by specific gravity. Oils, greases and light hydrocarbons are floated off in interceptors and separators under FPC Section 1003, whose opening requirement at 1003.1 is that interceptors and separators "shall be provided to prevent the discharge of oil, grease, sand and other substances harmful or hazardous to the public sewer, the private sewage system or the sewage treatment plant or processes." Section 1003.2 adds that the size, type and location of every interceptor must be approved by the plumbing official, that it be installed per the manufacturer's instructions, and that wastes not requiring treatment or separation shall not be discharged into any interceptor or separator — routing clean water through a grease interceptor short-circuits it.
3. Cooling. Temperature is reduced to the ordinance limit, and to below the 140-degree-F threshold of FPC 702.5 if standard-rated drainage piping is to be used downstream.
4. Neutralization. pH is corrected. The classic passive device is a limestone or marble chip neutralization basin filled with high-calcium-carbonate media, through which the acid stream percolates; active systems dose caustic or acid under pH control. Either way, FPC 803.1 requires the device to be automatically supplied with its neutralizing medium.
5. Equalization. A holding tank smooths a batch dump into a steady discharge rate so the treatment plant is not shocked.
6. Sampling and metering. A sampling manhole or sampling well on the discharge side lets the utility draw a compliance sample. Many Florida FOG and industrial ordinances make this mandatory.

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4. Drainage Design Details for Industrial Buildings

• Trench drains and floor drains in process areas are sized for the washdown flow rate, not for fixture units, and they feed the interceptor rather than the sanitary main directly.
• Keep clean water out of treatment. FPC 1003.2's prohibition on discharging untreatable wastes into an interceptor is the code version of an operating principle: every gallon of clean water routed through a separator reduces its retention time and its effectiveness.
• Backwater protection. Where fixtures or floor drains sit below the next upstream manhole cover, FPC Section 714 backwater valve requirements apply, and FPC Section 1101.9 extends the same requirement to storm drainage systems.
• Materials. Use FPC Table 702.1 for aboveground drainage and Table 702.2 for underground, then override for chemistry and temperature under 702.5 and 702.6. Where a corrosive stream and a hot stream coincide — a plating rinse at 160 degrees F, for example — the material must satisfy both.
• Venting. A chemical waste system has its own vent system, separate from the sanitary vents, in the same corrosion-resistant material.

[!WARNING] Air admittance valves and non-neutralized special waste do not mix. FPC Section 918.8 prohibits air admittance valves in non-neutralized special waste systems as described in Chapter 8, except where the valves comply with ASSE 1049, are constructed of approved corrosion-resistant materials, and are tested for chemical resistance to ASTM F1412. Dropping a standard AAV on a laboratory waste line is a rejectable installation.