Current through Register Vol. 41, No. 3, September 23, 2024
A. Conventional
sludge composting facilities aerobically process digested, or otherwise
treated, sewage sludge that is uniformly mixed with other organic materials and
bulking agents to facilitate biological decomposition of organics. The treated
sewage sludge will be exposed to temperatures at or above 55°C for three
consecutive days or more. The method of mixing and aeration, and the carbon to
nitrogen characteristics, of the compost mix are critical to the process
design.
B. General design. Unless
the facility is totally enclosed, an appropriate buffer shall be established on
a case-by-case basis by considering both the locations of any residential area,
hospitals, nursing homes for the elderly and serum production centers and the
prevailing wind at such locations. Local jurisdictions impacted by this
restriction shall be so notified.
1. All
compost facilities shall be provided with adequate means to prevent and control
odors as necessary.
2. All compost
facilities shall be provided with all-weather roads to and from the facility,
as well as between the various process operations.
3. The receiving, mixing, composting, curing,
drying, screening, and storage areas shall be paved with asphaltic concrete,
reinforced concrete, or other impervious, structurally stable material that
provides similar site characteristics.
4. The facility shall be graded to prevent
uncontrolled runoff and a suitable drainage system shall be provided to collect
all process wastewater and direct it to storage and treatment facilities.
Process wastewater includes water collected from paved process areas. The
capacity of the drainage system, including associated storage or treatment
works system shall be based on the 24-hour rainfall of a 10-year return
frequency.
5. All facility process
wastewater and sanitary wastewater shall be collected and treated prior to
discharge.
C.
Facilities. A weigh scale, volumetric method, or other means shall be provided
for determining the amount of sludge or residuals delivered to the facility and
the amount of compost material removed from the facility. Adequate space and
equipment must be provided for mixing operations and other material handling
operations.
1. Where liquid, or dewatered,
sludge or residuals are processed by the compost facility, all receiving of
such inputs shall occur in either:
a. An area
that drains directly to a storage, treatment, or disposal facility.
b. A handling area which shall be
hard-surfaced and diked to prevent entry of runoff or escape of the
liquids.
c. A sump with an
adequately sized pump located at the low point of the hard-surfaced area shall
be provided to convey spills to a disposal or holding facility.
2. Provisions for cleaning all
sludge transport or residual hauling trucks that return to public roads, shall
be provided at all compost facilities. The facility shall be capable of
effective operation regardless of weather conditions. Wash water shall be
collected for necessary treatment.
3. At all compost facilities handling liquid
or dewatered residual materials that must be mixed prior to composting, a
mixing operation shall be provided. The operation shall have sufficient
capacity to properly process the peak daily waste input with the largest mixer
out of operation. Volumetric throughput values used to establish necessary
mixing capacity may be based on the material volume resulting from the sludge
to bulking agent ratio, or may be estimated from previous experience or pilot
scale tests.
4. Effective mixing
equipment should be provided for use at all compost facilities. The ability of
all selected equipment to produce a compostable mix from sludge of an
established moisture content, residual material, and the selected bulking agent
shall be documented from previous experience or pilot tests.
5. Except for windrow composting wherein
mobile mixers are used, an area with sufficient space to mix the bulking agent
and sludge or residuals and store half of the daily peak input shall be
provided. The mixing area shall be covered to prevent ambient precipitation
from directly contacting the mix materials.
6. Where conveyors are used to move the
compost mix to the composting area and or help provide mixing, either
sufficient capacity shall be provided to permit handling of the mix with one
conveyor out of operation, or a backup method of handling or storing shall be
provided. Runoff shall be directed to a storage or treatment facility. Capacity
of the drainage system shall be based on the 24-hour rainfall producing a peak
rate expected once in 10 years.
D. System design. The system design shall be
sufficient to provide the level of treatment required for protection of public
health and welfare in relation to the anticipated management method.
Consideration should be given to covering the compost mixing pad and curing
area in order to allow for handling of bulking agents and treated sludge and
the finished compost, during extended periods of precipitation. If a roof type
cover is not provided, operation of the facility during critical weather
periods shall be addressed. Sufficient equipment shall be provided for
routinely measuring the temperature and oxygen at multiple points and depths
within the compost piles.
1. Windrow method.
The area requirements shall be based on the average daily compost mix inputs, a
minimum detention time of 30 days on the compost pad, and the area required for
operation of the mixing equipment. Sufficient compost mix handling equipment
shall be provided to turn the windrows daily. In addition, proper drainage and
space shall be provided to allow equipment movement between compost pile
sections and access around the working areas.
2. Aerated-static pile method. The
aerated-static pile area requirement shall be based on the average daily
compost mix inputs, along with storing base and cover material, with a
composting time of 21 days, unless the applicant can demonstrate through
previous experience or pilot scale studies that less time is necessary to
achieve the requirements.
a. The compost mix
pile shall be provided with a means of uniformly distributing air flow. One
foot or more thick base of friable material may be utilized under the deepest
sections of compost mix. A 1-1/2 foot or more thick covering blanket of
unscreened compost or a one foot thick or more blanket of screened compost may
be utilized over the compost mix pile.
b. Compost mix piles should be configured to
provide adequate aeration of the mix using either positive or negative pressure
for air flow through the piles.
3. Confined composting methods. Due to the
large variation in composting processes, equipment types, and process
configuration characteristic of currently available confined systems, such as
enclosed operations or in-vessel systems, it is not feasible to stipulate
specific design criteria. However, a confined composting system will not be
approved unless the applicant can demonstrate, through previous operating
experience or pilot scale studies, that the material removed from the enclosed
container or compost process, after the manufacturer's suggested residence
time, has an equivalent or higher degree of stabilization than would be
achieved after 21 consecutive days of aerated static pile composting.
E. Aeration. Sufficient blower
capacity shall be provided to deliver the necessary air flow through the
compost mix, but the delivered air flow shall not be less than a minimum
aeration rate of 500 cubic feet per hour per dry ton (CFH/DT). Where
centralized aeration is utilized, multiple blower units shall be provided and
shall be arranged so that the design air requirement can be met with the
largest single unit out of service. Where individual or separated blowers are
used, sufficient numbers of extra blowers shall be provided so that the design
air requirement can be met with 10% of the blowers out of service. For
facilities that are not continuously manned, the blower units should be
equipped with automatic reset and restart mechanisms or alarmed to a
continuously manned station, so that they will be placed back into operation
after periods of power outage.
1. Each pile
aeration distribution header shall be provided with a throttling control valve.
The aeration system shall be designed to permit both suction and forced
aeration. The piping system shall be capable of delivering 150% of the design
aeration rate. The aeration piping may be located in troughs cast into the
compost pad.
2. The aeration system
shall be designed to permit the length of the aeration cycle to be individually
adjusted at each pile header pipe.
F. Compost handling. The design of the curing
area shall be based on a minimum retention time of 30 days unless the applicant
can demonstrate through previous experience or pilot studies that less time is
required. Daily input shall be based on the average daily input of mix to the
composting area.
1. A drying stage is
optional, but is usually required if compost is to be recycled as a bulking
agent or if screening is required. Consideration should be given to covering
the drying area. If a cover is provided, it can be designed so that sunlight is
transmitted to the composting materials while preventing direct contact with
ambient precipitation. Efficient drying may be accomplished by drawing or
blowing air through the compost mixture or by mechanical mixing of shallow
layers with stationary bucket systems, mobile earth moving equipment, or
rotating discs.
2. Screening shall
be provided for all compost facilities where the compost disposition
necessitates the use of a screened product or where the bulking agent must be
recycled and reused. When dry compost is used as a bulking agent screening is
not typically provided.
a. A daily screening
capacity of 200% of the average daily amount of compost mix shall be provided
when screening is required.
b.
Based on previous composting facility performance, or on pilot tests, the
ability of the specified equipment to screen compost at the projected moisture
range shall be demonstrated.
c. The
area used for screening should be covered unless operations are not hindered
when screening is temporarily discontinued.
3. Storage areas shall be provided for six
months storage of compost unless the applicant can demonstrate (through
previous experience, pilot studies or letters of intent to accept compost
offsite) that less storage area is required. Storage for curing or drying
biosolids compost is usually provided if compost is to be recycled for public
use.
For all compost facilities where a separate bulking agent
is required, storage area for a six-month supply of the bulking agent shall be
provided, unless the applicant can demonstrate that bulking agent supplies can
be replenished more frequently.
Statutory Authority
§ 62.1-44.15 of the Code of Virginia.
