A. Stabilization. Biosolids treatment processes are primarily designed to increase the solids content of the biosolids by separation and removal of liquid and are designed to stabilize the solid fraction through biochemical conversions that inactivate pathogens and reduce vector attraction characteristics and the potential for odor production. Such treatment should be designed to improve the characteristics of the biosolids for a particular use/disposal practice, increase the economic viability of using a particular practice and reduce the potential for public health, environmental and nuisance problems.
B. Class I treatment. Class I treatment may be achieved by process sequences to further reduce (PFRP) or eliminate pathogens, i.e., Class A pathogen control. Class I treatment methods reduce all pathogens potentially contained in biosolids or septage to a level below specified limits (Table 3). Class A microbiological standards and an acceptable solids content shall be achieved at the time biosolids are used or prepared for distribution or marketing in accordance with the appropriate management practices specified in this chapter. Class I treatment processes should include one or more of the following operations:
1. Heat treatment. The temperature of the biosolids that is used or disposed is maintained at a specific value for a specified period of time:
a. When the percent solids of the biosolids is 7.0% or higher, the temperature of the biosolids shall be 50°C or higher; the time period shall be 20 minutes or longer; and the temperature and time period shall be determined using equation B-1, except when small particles of biosolids are heated by either warmed gases or an immiscible liquid.
Equation B-1: D1 = (131,700,000)/ 10(exp 0.1400(t))
D1 = time in days that biosolids temperature is t or more
t = Biosolids temperature in degrees Celsius (°C).
exp = exponent or power that Base 10 is raised to.
b. When the percent solids of the biosolids is 7.0% or higher and small particles of biosolids are heated by either warmed gases or an immiscible liquid, the temperature of the biosolids shall be 50°C or higher; the time period shall be 15 seconds or longer; and the temperature and time period shall be determined using equation B-1.
c. When the percent solids of the biosolids is less than 7.0% and the time period is at least 15 seconds, but less than 30 minutes, the temperature and time period shall be determined using equation B-1.
d. When the percent solids of the biosolids is less than 7.0% the temperature of the biosolids is 50°C or higher; and time period is 30 minutes or longer, the temperature and time period shall be determined using equation B-2.
Equation B-2: D2 = (50,070,000)/ 10(exp 0.1400(t))
D2 = time in days that biosolids temperature is t or more
t = Biosolids temperature in degrees Celsius (°C).
e. The temperature of the biosolids is maintained at 70°C or higher for a time period of 30 minutes or longer (Pasteurization).
2. Heat drying. A process wherein dewatered biosolids cake is dried by direct or indirect contact with hot gases and the biosolids moisture content is reduced to 10% or lower. Direct drying is achieved when the biosolids particles reach temperatures of 80°C or higher. Indirect drying may involve the temperature of the gas stream measured at the point where the gas stream leaves the dryer. Indirect drying may be achieved when the wetbulb temperature of the gas stream leaving the dryer is in excess of 80°C or the biosolids particles reach temperatures of 80°C or higher.
3. Thermophilic composting. A process using the within-vessel composting method which maintains a treated biosolids temperature of 55°C or greater for three days. A process using the static aerated pile composting method which maintains a treated biosolids temperature of 55°C or greater for three days. A process using the windrow composting method which maintains a treated biosolids temperature at 55°C or greater for at least 15 days during the composting period, and during the indicated high temperature period, there is a minimum of five turnings of the windrow. Operating temperatures are measured at the depth of 30 cm from the surface of the compost mixture. As thermophilic composting processes are less efficient in destroying pathogens than other disinfection processes an additional storage of processed compost up to 30 days or more may be necessary to achieve an adequate level of vector attraction reduction as verified by testing prior to final disposition (Table 3).
4. Thermophilic aerobic digestion. Liquid biosolids consisting of 50° or more waste biological liquid by dry weight, is agitated with air or oxygen to maintain one mg/l or more dissolved oxygen at mid-depth, during a mean cell residence time of 10 days or more at 55°C or more.
5. Alkaline (PFRP) stabilization. Thorough blending of an alkaline additive to digested biosolids in sufficient quantities to produce a mixture pH of 12 or more for a period of 72 hours or more with one of the following: (i) mixture temperature of 55°C for a minimum period of 12 hours, (ii) mixture temperature of 70°C or more for a minimum period of 30 minutes or more. Such treatment may be followed by storage for an acceptable period of time to dry the mixture to an adequate dry solids content. Alkaline addition to undigested biosolids will be considered on a case-by-case basis with extensive monitoring used to verify the level of pathogen control achieved.
6. Chlorine oxidation. A process of introducing high doses of chlorine (1,000 mg/l to 3,000 mg/l) into the biosolids stream under low pressure (30 psig or more) producing a biosolids pH of four or less in order to achieve Class A microbiological standards (Table 3), followed by acceptable drying to achieve a suspended solids content of 30% or more.
7. Alternative equivalent stabilization processes. The process operating parameters for alternative equivalent stabilization processes (PFRP) should be addressed, case-by-case, based on division evaluation of the results of adequate monitoring and testing programs (Table 3), with input from the USEPA staff, i.e., the Pathogen Equivalency Committee.
C. Class II treatment. Class II Treatment may be achieved by Process Sequences to Significantly Reduce Pathogens (PSRP), i.e., Class B Pathogen Control. Class II treatment methods reduce bacteria (fecal coliform, fecal streptococci, enterococci) found in the treated biosolids or septage 1 logs or more (32 fold) below the densities found in the raw biosolids to achieve a density of (6.3 log10 per gram of total solids or less (Table 3)). Class B microbiological standards shall be achieved at the time the biosolids are removed and transported for land application in accordance with the management practices specified. Class II treatment processes may include one or more of the following operations:
1. Anaerobic digestion. A process whereby biosolids are maintained in an anaerobic environment for a mean cell residences period ranging from 60 days at 20°C to 15 days at 35°C.
2. Aerobic digestion. A process of agitating biosolids with air or oxygen to maintain aerobic conditions for a mean cell residence period ranging from 60 days at 15°C to 40 days at 20°C.
3. Low-temperature composting. A process using the within-vessel, aerated static pile or windrow composting methods, whereby the temperature of treated biosolids is maintained at a minimum of 40°C for five days. For four hours during this period the operating temperature of the treated biosolids exceeds 55°C. Additional storage of processed compost for 30 days or more may be necessary to provide the necessary level of vector attraction reduction prior to final disposition.
4. Alkaline (PSRP) stabilization. A process where sufficient alkaline additive is blended with unstabilized biosolids to produce a minimum mixture pH of 12 after two hours of contact and a pH of 11.5 or more for 22 additional hours or more, with storage for a period sufficient to produce an acceptable dry solids content as necessary for the method of final disposition.
5. Air drying. Biosolids treated by methods similar to those listed above, but not meeting Class II treatment standards are dried on sand beds or in basins with underdrains for a minimum period of three months, during which time the ambient daily temperature exceeds 0°C and a dried biosolids are produced.
D. Additional treatment methods to provide disinfection of treated biosolids. Pathogen treatment processes may be enhanced by providing additional treatment methods to eliminate parasitic worms and ova (EH process sequence). Any of the processes listed below, if added to stabilization processes described previously, will further lower pathogens. Because these processes, when used alone, do not reduce nuisance odors and the attraction of vectors, they are considered to be supplementary to typical stabilization and pathogen treatment processes.
1. Beta Ray Irradiation. A process involving the irradiation of biosolids with beta rays at dosages of at least one megarad at 2°C.
2. Gamma Ray Irradiation. A process involving the irradiation of biosolids with gamma rays from certain isotopes, such as 60Cobalt and 137Cesium, at dosages of at least 1.0 megarad at 20°C.
E. Vector attraction reduction parameters. One of the appropriate vector attraction reduction requirements shall be achieved and Class A or B pathogen control obtained when bulk biosolids are applied to agricultural land, forest, a public contact site, reclamation site, lawn or home gardens. One of the appropriate vector attraction reduction requirements shall be met when Class A biosolids are sold or given away in a bag or other container for application to the land. The following operational methods will achieve the necessary vector attraction reduction requirements:
1. The mass of volatile solids in the biosolids shall be reduced by a minimum of 38% (see calculation procedures in "Environmental Regulations and Technology—Control of Pathogens and Vector Attraction in Biosolids," EPA-625/R-92/013, 1992, U.S. Environmental Protection Agency, Cincinnati, Ohio 45268).
2. When the 38% volatile solids reduction cannot be met for an anaerobically digested biosolid, vector attraction reduction can be demonstrated by digesting a portion of the originally digested biosolids anaerobically in the laboratory in a bench-scale unit for 40 additional days at a temperature between 30°C and 37°C. When at the end of the 40 days, the volatile solids in the biosolids at the beginning of that period is reduced by less than 17%, adequate vector attraction reduction is considered demonstrated for the originally digested biosolids.
3. When the 38% volatile solids reduction requirement cannot be met for an aerobically digested biosolid, vector attraction reduction can be demonstrated by digesting a portion of the originally digested biosolids that has a percent solids of 2.0% or less aerobically in the laboratory in a bench-scale unit for 30 additional days at 20°C. When at the end of the 30 days, the volatile solids in the biosolids at the beginning of that period is reduced by less than 15%, adequate vector attraction reduction is considered demonstrated for the originally digested biosolids.
4. The specific oxygen uptake rate (SOUR) for biosolids treated in a Class II or better aerobic process shall be equal to or less than 1.5 milligrams of oxygen per hour per gram of total solids (dry weight basis) at a temperature of 20°C.
5. Biosolids shall be treated in a Class II or better aerobic process for 14 days or longer. During that time, the temperature of the biosolids shall be higher than 40°C and the average temperature of the biosolids shall be higher than 45°C.
6. The pH of treated biosolids shall be raised to 12 or higher by alkaline addition and, without the addition of more alkaline material, shall remain at 12 or higher for two hours and then at 11.5 or higher for an additional 22 hours. Alkaline stabilization of untreated biosolids shall be evaluated on a case-by-case basis.
7. The percent solids of treated biosolids that does not contain unstabilized solids generated in a primary wastewater treatment process shall be equal to or greater than 75% based on the moisture content and total solids prior to mixing with other materials.
8. The percent solids of treated biosolids that contains unstabilized solids generated in a primary wastewater treatment process shall be equal to or greater than 90% based on the moisture content and total solids prior to mixing with other materials.
9. For biosolids that are surface applied and incorporated, or injected, below the surface of the land:
a. No significant amount of the biosolids shall be present on the land surface within one hour after the biosolids are injected.
b. When the biosolids that are injected below the surface of the land are Class A with respect to pathogens, the biosolids shall be injected below the land surface within eight hours after being discharged from the pathogen treatment process.
c. Biosolids applied to the land surface shall be incorporated into the soil within six hours after application to or placement on the land.
d. When biosolids that are incorporated into the soil are Class A with respect to pathogens, the biosolids shall be applied to or placed on the land within eight hours after being discharged from the pathogen treatment process.
10. The pH of untreated domestic septage applied to land shall be raised to 12 or higher by alkaline addition and, without the addition of more alkaline material, shall remain at 12 or higher for 30 minutes prior to application.
§32.1-164.5 of the Code of Virginia.
Derived from VR355-17-200 §3.15, eff. January 25, 1995; amended, Virginia Register Volume 13, Issue 26, eff. October 15, 1997.