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FY 1990 ABSTRACTS
FY 1990 Water Problems and Issues
During this current period of
economic recession and low population growth, the State of New
Hampshire now has time to regroup and check its environmental pulse.
In the early 1980's, rapid growth led to "knee jerk" responses
to development. Now that the pressure is off of State and local
planning and conservation agencies, a critical review of rules
and regulations will afford environmentally sound growth in the
future, without unrealistic hardship posed to select individuals.
At the core of this process must be substantial data collection
efforts at both intermittent and continuous time intervals. This
data allows a proper quantitative assessment of background conditions,
effects of change and long term trends. This information will then
allow a cause/effect relationship to be identified when reviewing
policy and development.
Surface Water Quantity
It is difficult for the vast majority of the New Hampshire population to understand
that they, too, are susceptible to drought conditions. In the broad context
here, drought signifies that not all demands are being met. When one considers
the multi-objective uses of New Hampshire surface waters (hydropower, aquatic
habitat and other instream flows as well as water supply) , many streams
are at their limit of reliable supply. This is especially true for water
recreation, which is seeing increasing conflicts over competitive uses. In
addition, although hydropower development appears to be a desirable energy
form, it is meeting with stiff resistance from riparian landowners. The State
is currently bordering on 100-year drought conditions. Important surface
water quantity issues include: flow duration information from ungaged watersheds,
water availability, dam safety analyses, ground water contributions to surface
water, ground water contributions to wetlands, and instream flow requirements.
Surface Water Quality
There is modest information about the quality of surface waters in the state.
This type of information is usually gathered with a specific project in mind
or as a one-time exercise. In general, the state's surface water quality
can be rated as fair to good. Surface water contamination is related to point
sources (such as sanitary sewer outfalls or combined sewer outfalls) and
nonpoint sources (for example, contaminated groundwater seepage, agricultural
or silvicultural runoff, or acid rain). Existing ambient water quality conditions
must be established, otherwise the identification of contamination sources
is difficult to address. The ultimate transport and fate of contaminants
in surface waters affects all aspects of social and environmental systems
and in New Hampshire deserves attention. Identifying the sources of contamination
is one item, but it must be matched with a proper evaluation of the consequences
and remedial measures. Important surface water quality issues include: nonpoint
source pollution control, eutrophication, ambient/ existing water quality
conditions, waste load allocation of water bodies, environmental effects
of recreation, and local planning requirements for water quality protection.
LAND
APPLICATION OF MUNICIPAL SLUDGE IN NEW HAMPSHIRE FORESTS: MINIMIZING
THE RISKS TO GROUNDWATER QUALITY
Investigators: Dr. William B. Bowden and Dr. C. Tattersall
Smith
Descriptors: groundwater quality, sludge, leaching, nutrients, nitrogen
Problem and research objectives
The New England region is experiencing a rapid decline in the availability
of landfill space to dispose of wastes generated by society. One solution is
to reserve this limited space for highly toxic substances and to recycle appropriate
wastes in beneficial ways. Municipal sludges constitute a significant volume
of wastes that have in the past been landfilled, incinerated, or dumped in
the ocean; practices that each have growing social and legal problems. As an
alternative, some municipal sludges contain valuable nutrients and little or
no toxic materials, and might be applied on nutrient-poor forest lands to improve
soil conditions or to promote tree growth. However, to be a viable alternative,
it is essential to establish that forest land application does not adversely
affect ground and surface water quality, soil chemical characteristics, changes
in plant species composition, or tree growth rates. In general, surface and
groundwater contamination from land application of sludge can be minimized
if sludge loading and mineralization rates do not exceed the capacity of the
soil and vegetation to store various sludge constituents. Specifically, we
hypothesize that if sludge applications are managed to minimize nitrate leaching,
this will coincidentally minimize impacts due to phosphate, heavy metals, and
toxic organic compounds, since nitrate is more mobile than most other sludge-derived
constituents.
Principal Findings and Significance:
Soil solutions
Nitrate-N has been virtually undetectable in soil solutions
from the untrenched (i.e. undisturbed, vegetated) areas of all treatment
plots. In contrast, nitrate levels within the trenched (i.e. non-vegetated)
areas began to increase dramatically in the fall of 1989, about 3-4
months after the sludge was applied. This result indicates that tree
uptake can effectively block N mobility even at the 800 kg N/ha level.
Once the tree barrier is removed (as in the trenched areas), ammonium
from mineralization of the organic-N in the sludge is rapidly nitrified
to mobile nitrate.
Our data indicate that cation exports from the trenched areas (dominated
by Ca++ and Na+) are largely balanced by N03-, Sulfate, followed
by Cl-, are the next most important anions in the trenched soil solution.
In the untrenched soil solutions, where nitrate is rarely present,
sulfate dominates the anions, followed by chloride. Phosphate was
never above detection limits in any lysimeter or treatment. Total
alkalinity was measured in samples after April 1989 but tends not
to contribute much to the anion sum. It is generally less important
than chloride on a total charge basis. Ammonium was less abundant
than any of the base cations in soil solution.
There was a highly significant, positive relationship between nitrate
leaching and cadmium and zinc leaching. In contrast, we found no
significant relationship between nitrate leaching and copper or lead
leaching. We can not detect either nickel or chromium in our leachates.
At low nitrate leaching levels, leaching of all six measured metals
was also low.
Vegetation
Sludge additions clearly increased the nitrogen content of the
overstory beech trees. Qualitative measurements indicate that the
herb biomass (which was small initially) have not changed.
Soils
Analysis of all three soil samples data sets is complete for
total Kjeldahl nitrogen, total phosphorus, and DTPA extractable metals.
Data reduction of these analyses is currently under way. Exchangeable
cations will be analyzed on selected samples, this fall.
Nitrogen mineralization
Mineralization rates were highest in the surface sludge/organic
horizon samples during the summer and fall following sludge application.
Deeper mineral soils had small amounts of either mineralization or
immobilization during the August/September sampling period. Ammonium
production peaked in the surface horizons (0 cm) during the first
sampling period (July) for all treatments except for the control,
which peaked during the second sampling period (August/September).
During the first incubation period, ammonium production increased
in direct relation to the amount of sludge originally added; controls
had the lowest rates and the 800 kg N/ha treatment had the highest.
Nitrate production was negligible during the first sampling period
and peaked during the second, again in the surface horizons, for
all treatments. Nitrate production was greatest in the mid-level
(400 kg N/ha) treatment rather than the high-level (800 kg N/ha)
treatment, suggesting the possibility that there was some inhibition
of nitrification at the high loading rates.
Our data suggest that, as long as the loading rates are below 800
kg TKN/ha (operationally 400 kg TKN/ha might be a better target rate)
and tree uptake is adequate, sludge applications should not lead
to unacceptably high levels of nitrate leaching. Sludge additions
stimulated nitrogen mineralization in surface soil horizons, for
a short period of time. However, plant uptake was sufficient to minimize
nitrification of this ammonium to nitrate, and so, prevented nitrate
leaching. Furthermore, there appeared to be little or no mobility
of other nutrients. Phosphate was virtually immobile. Base cation
mobility was acceptably low, excepting calcium, which was added in
enormous quantities in the sludge. Of the six heavy metals measured,
only cadmium and zinc increased with nitrate leaching. Both metals
remained below the current ambient water quality standards, even
at high nitrate leaching levels.
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ANTHROPOGENIC EFFECTS ON NEW HAMPSHIRE SURFACE WATER QUALITY:
LONG TERM EVIDENCE FROM LAKE SEDIMENTS
Investigators: Henri E. Gaudette, and W. Berry Lyons,
University of New Hampshire
Descriptors: Trace Metals, Lake Sediments, Accumulation, Landfills, Water Quality,
Water Use.
Problem and Research Objectives:
The purpose of this study is to determine the impacts from a sanitary landfill
to the sediments of a stream and pond. The Turnkey Landfill of Danbury, NH,
which has been established as a source of organic and metal contaminants, is
located in an abandoned sand and gravel pit just west of US route 4 and adjacent
to Frazier Brook in west central New Hampshire. This unlined landfill was in
operation from 1976 to 1986 when it was closed and capped with a clay and vegetative
cover.
Possible environmental impacts were first indicated in the Spring
of 1981 by the discoloration of Frazier Brook, approximately 100
meters west of the landfill. By 1984 the discoloration of Frazier
Brook had extended to Eagle Pond approximately 2.4 km south, initiating
an application of potassium permanganate and aluminum sulfate, ordered
by the New Hampshire Water Supply and Pollution Control Commission,
in order to precipitate the contamination out of the surface water.
Subsequent repetitive water samples from the brook and pond have
shown a general decrease in the levels of organic and metal contaminants
since the application in 1984 and the closure in 1986. The sediments
of the brook and pond have not, however, ever been investigated.
The main questions of this research are what are the quantities
of contaminants in the sediments of Frazier Brook and Eagle Pond
and how are they distributed spatially in the brook and pond system.
Principle Findings and Significance:
The groundwater flow direction, hydraulic gradient and flow rate through the
landfill show a slight variability due to seasonal water table fluctuations.
The direction of groundwater flow is generally east to west through the landfill
and perpendicular to Frazier Brook. The groundwater hydraulic gradient and
flow rate were estimated to have long term average values of 0.025 m/m and
2300 m3/d (0.027 m3/s) respectively.
The seepage meter and piezometer data suggest that leachate is still
being generated at the landfill and incorporated into the groundwater
which is then being discharged into Frazier Brook at an average rate
of 0.030 m3/s. The long term mean annual flow of the brook in the
vicinity of the landfill and discharging into Eagle Pond was determined
to be 0.2 and 0.89 m3/s respectively.
The results of the sediment metal (aluminum normalized) concentrations
show the majority of sediment samples to be enriched in all metals.
The one exception is chromium which is not enriched in any of the
samples. Analysis of 137Cs and 21OPb from Core C was used to estimate
a sedimentation rate for Eagle Pond of 0.50 and 0.76 cm/yr respectively
and to determine a time sequence for Cores A and B. The metal concentrations
versus depth and time profiles show that the influence of the landfill
on the sediments is much higher than the ambient concentrations and
has remained fairly constant since the landfill began operating in
1976. Therefore, the closure of the landfill, and the preventive
steps which have been taken since closure, have not mediated the
chemical impact of the landfill upon the stream and lake sediments.
Our chemical data suggest that the landfill contaminants still exist
in quantities in the upper portions of the lake sediments to pose
a significant concern should environmental conditions change sufficiently
to cause re-mobilization of these contaminants.
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OIL SPILL RESPONSE ENGINEERING AND PLANNING
Investigators: M.
R. Swift and Barbaros
Celikkol, University
of New Hampshire
Descriptors: Estuaries, oil-water interfaces, coastal engineering, pollution
control, estuarine modeling, port facilities, fluid flow, dynamic programming
Problem and research objectives
Tanker and barge traffic associated with the five petroleum product terminals
along the NH side of the Piscataqua River represents a constant oil spill threat
to the contiguous Great Bay System, NH, an estuarine reserve. Several serious
accidents have in fact taken place in the 1970's and two small spills in 1990.
A major factor is that the Piscataqua channel is subject to high velocity tidal
currents. Should a spill occur, problems arise in knowing where the slick will
move and how to control it using booms.
In this project, these problems were addressed by developing procedures
for using diversion booms in high speed current environments and
in revising and implementing a previously developed Oil Spill Trajectory
Model. In the diversion boom concept, the boom is angled to the current
in order to direct the slick to one side rather than attempt to contain
the oil at an apex. Boom configuration (planform shape) must be designed
before an emergency in order to prevent leakage when deployed. The
Trajectory Model computer program makes use of surface current data
to calculate the movement and spreading of spills in the Great Bay
System.
Principal findings and significance
The boom configuration analysis models were completed in a format easy for
the user to employ for design purposes. Model predictions agreed well with
the experimental data from the boom shape experiments.
Boom configurations designed using the software package behaved
as expected in demonstration experiments. The deployed boom was stable
and could divert surface pollutants to shore-side skimming equipment.
Use of the bottom screw-in anchor was not successful, and portable
anchor performance in the high currents of the Piscataqua was inconsistent
depending on whether it set properly or not. Permanent moorings or
systems secured to the berthed vessel are recommended. At the river
and creek tributary locations where the currents are slower, an 85
lb. Danforth was found sufficient for holding protective booms in
position.
The Trajectory Model was found
to be a useful tool in planning a "Table-Top" exercise
conducted by the DES. The spill response scenario involved the
terminal operators, the U.S. Coast Guard, the U.S. Navy, as well
as local fire and police departments. The upgraded oil spreading
algorithm and enhanced graphics made the Trajectory Model especially
effective.
Boom designs and methods of deployment developed in this project
are now informally part of the area's contingency plans. The work
will be incorporated formally in future documents mandated by recent
government action.
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EVALUATION OF THE ENVIRONMENTAL IMPACTS RESULTING FROM MOTOR
BOAT ACTIVITIES - PHASE I
Investigator: Thomas
P. Ballestero, University of New Hampshire
Descriptors: Aquatic Plants, Boating, Economics, Lakes, Plant Stress, Pollution
Control, Recreation
Problem and Research Objectives:
Due to the expanding population and increased environmental concerns yet
finite water resources, use of New Hampshire water resources for recreational
purposes is becoming a focal point of disagreement. A case in point is
personal water craft use (jet skis). The personal water craft (PWC) is
classified by the Coast Guard as a motor boat. PWC bans on ponds and lakes
are increasing, often with environmental justification. Yet, on these same
water bodies, other pleasure motor craft are still allowed. A critical
question, therefore, is "What are the typical environmental consequences
of various recreational craft on the water column as well as on flora and
fauna?"
The nature of this first phase of research was a literature review.
The review delineated the current body of knowledge regarding the
environmental effects of propeller and hydraulic jet pleasure craft.
This phase paves the way for the second phase, which will be a field
testing of various water craft and the measurement of their environmental
effects.
Principal Findings to Date:
General Information
Most of the general information material originated from nontechnical
sources, i.e., newspapers, news magazines, manufacturers' journals,
etc.; however, some technical articles were included in this category.
Themes that were also present in this category included: regulation
of ski craft, utility of ski craft, introduction to ski craft, production
literature, common ski craft criticism and important issues surrounding
the regulation of ski craft use.
An important subliminal message in articles berating ski craft is
not so much at issue with the machine itself as with the operator.
There would appear to be a derogatory typecast of ski craft operators
which has no documented logical basis. The typecast seems to be that
of one who is not concerned at all with impacts on the environment
and/or consideration of others.
Turbulence and the Effect of mixing on sediments and Microorganisms
Researchers have documented relations between motor boat activities
and turbidity (suspended sediments in the water column). In few cases
have researchers looked at specific motor boat types (inboard versus
outboard, propeller versus jet) and ensuing consequences. However,
variables which repeatedly are related to increased turbidity levels
are: water depth, boat (horse)power, amount of boat traffic, and
bottom sediment characteristics. Here, the engine thrust (propeller
or jet) is dispersed into the water column. When this thrust dispersion
reaches the water body floor, sediments may be moved. Once sediments
are resuspended from the bed, there may be a host of subsequent consequences
such as: reduced light penetration, increased nutrient concentration
and increased micro-organisms.
Boating Effects on Fish and Aquatic Plants
Two primary subclasses in this category are direct and indirect effects. Direct
effects result from immediate contact of boats or boat turbulence on fish
and aquatic plants. Indirect effects stem from the secondary effects of boat
traffic; for example, resuspending sediment which, in turn, reduces light
penetration into water which, in turn, is disruptive to macrophytes.
The indirect effects of the types of water quality problems associated
with motor boats (sediment re-suspension, turbulence, increase in
dissolved oxygen) have been extensively studied. That is, there are
numerous studies relating to the effects of silt and sediment on
aquatic flora and fauna. No studies have documented the effects of
ski craft on sediment resuspension or their indirect effects on fish
and aquatic plants. No studies have documented the relative indirect
effects of ski craft and motor boats.
The direct effect of turbulence on fish is manifested in increased
mortality of fish species and eggs; mortality being directly related
to the intensity of the turbulence.
Pleasure Boats and Water Pollution
As the ski craft is a relative newcomer to water recreation,
no literature could be found which documented water pollution resulting
from them. However, a large body of literature has been presented,
since the 1950's, concerning water pollution from pleasure craft.
There are two basic classes of water pollution in this category:
overboard discharges and exhausts.
Boating Impacts on Water Fowl
There are many human interferences in and around lakes and ponds
which may have effects on water fowl population, diversity and mortality.
These human interferences include: land development, recreation on
the water and on riparian lands, water development, and resources
development. To account for or isolate the effects of boating on
water fowl, typically researchers will perform enumeration studies
either over time at a fixed location or at various locations during
a similar time frame. The environments studied in these cases have,
in the former, boating increasing with time, or in the latter, locations
with and without boating. Of course, it is very difficult to control
all other human-related variables in these studies, however, there
do appear to be certain trends, for certain species, relating boating
activity to effects on water fowl. Also, timing of disturbances seems
to be important for certain species in that a critical time is during
the nesting selection period.
Mortality of water fowl due to motor boat activity was never reported
for any species; that is, what fraction of the total population is
killed by motor boats. However, when evaluating discovered carcasses,
motor boats can represent a significant percentage of water fowl
deaths. This type of sampling can be severely biased in that carcasses
resulting from motor boat injuries are easier to find than those
where the effect occurred at the water (i.e., toxicity) and the carcass
exists far from the water due to water fowl mobility.
Recreation/Water Resources Economics and Management
A current mindset is that when viewing humans and nature,
humans are not members or participants, but rather, consumers.
In this vein, all human activity is disruptive or destructive to
nature. Current environmental policy and philosophy seems to be
refuting this concept. The "no net loss of wetlands" policy
is a case in point. The mindset pits those who pursue less harmful
activity (i.e., birdwatching) against those who pursue more harmful
activity (i.e., dredging). This all falls into the development
of management strategies not only at the federal level, but at
the local level. Such planning activity reduces conflict by delineating
the range and utility of all recreational uses of water resources.
These strategies must also be compatible with maintenance of existing
environmental conditions.
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SAMPLING PROGRAM DEVELOPMENT AND PERFORMANCE EVALUATION
OF POINT OF ENTRY (POE) TREATMENT UNITS INSTALLED AT GASOLINE-CONTAMINATED
WELL SITES
Investigator: James P.
Malley, University of New Hampshire
Descriptors: Gasoline, Groundwater Pollution, Treatment, Aeration, Activated
Carbon
Problem and Research Objectives:
USEPA estimates that there are over 1.5 million underground storage tanks (UST)
in the United States containing hazardous substances or petroleum, and as many
as 200, 000 of these may be leaking. A recent study in Suffolk County, NY found
that 17% of the 500 UST recently removed showed signs of leaking. Of particular
concern are petroleum storage tanks which are ubiquitous due to our reliance
upon oil and gasoline. In many instances, contamination of drinking water supplies
from leaking UST affect individual wells in rural areas. Contamination of private
wells presents unique problems for regulatory agencies and utilities. Typically,
bottled water is provided for drinking as a short-term measure while an alternate
supply is located. However, bottled water is a costly solution and does not
reduce the health effects from inhalation or dermal exposure when the contaminated
water is used for other domestic purposes (e.g., bathing). In addition, the
political, legal, economic and technical constraints involved in remediation
of leaking UST may delay the securing of an alternate water supply for years.
A potential solution to individual well studies of VOC contamination and treatment
of public water supplies are reported in the literature; there is little information
about factors which affect design and performance of POE systems. Further,
few studies have addressed the effects of non-purgeable dissolved organic carbon
(NPDOC) and microbial activity on VOC treatment systems.
The research reported is part of an ongoing two-year study funded
by the New Hampshire Department of Environmental Services to evaluate
the use of point-of-entry (POE) treatment techniques for removing
petroleum contamination from individual wells. The main objective
of the study is to relate spatial and temporal variations in ground
water quality (e.g., VOC, NPDOC, microbial numbers) to the selection,
design and preformation evaluation of POE systems.
Principle Findings to Date:
Raw Water Quality:
Experimental data collected, for the first one-hundred days
of operation, show several interesting trends in raw water quality.
First, there are significant and rapid temporal changes in raw water
concentrations of VOC's, NPDOC, iron, manganese and microbial numbers
(HPC) at virtually all sites. Second, study sites which are located
in the same contaminant plume show significant spatial changes in
the type and concentration of contaminants. Results from samples
collected on the same days at two wells located approximately 100
meters apart and screened at the same elevation show up to one order
of magnitude difference in contaminant concentration. Third, virtually
all contamination sites have elevated levels of NPDOC with several
exceeding 3 mg/L for three times the background levels found in New
Hampshire. GCMS results indicate that the majority of the NPDOC is
MTBE and hydrophilic, non-volatile petroleum hydrocarbons. Fourth,
microbial activity is measured by R2A, HPC ranges from 1 x 105 to
3 x 106 CFU/100 ml and, in most cases, is well above typical levels
(104 CFU/100 ml) observed in New Hampshire ground water. Relationships
between VOC concentrations, NPDOC, microbial activity and other water
quality parameters are being investigated and will be discussed in
the final report.
POE System Performance:
Preliminary analysis of POE performance indicates that the aeration
system is insensitive to changes in raw water BTEX concentrations.
Consistently high (>90%) removals by aeration, despite significant
variations in raw water concentrations of benzene, toluene and xylene,
were observed at all sites. The flexibility of the bubble plate unit
is not surprising since it operates at a volumetric air/water ratio
above 160/1.
POE systems containing GAC are affected by the variations in VOC
and NPDOC. The NPDOC has a significant effect on the carbon bed life.
During the first year of study, the GAC was replaced to significant
MTBE breakthrough at three of the POE sites. BTEX compounds will
control selection, design and operation of the POE systems, particularly
when GAC units are used.
An economic evaluation of POE
systems is being performed focusing on capital and operation and
maintenance (O&M) costs. Field data
collected to date indicates POE system power costs range from $0.30
to $0.50 per thousand gallons treated. Capital cost data and maintenance
records for each unit are being compiled and cost data will be presented
in the final report at the end of the two-year study.
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EVALUATION AND AUTOMATION OF SMALL PRESSURE FILTER SYSTEMS
Investigators: Thomas
P. Ballestero and M.
Robin Collins, University of New Hampshire
Descriptors: Pressure Filter Automation, Infiltration, Water Quality Control
Problem and Research Objectives:
Recent passage of amendments to the Safe Drinking Water Act required the USEPA
to specify where filtration of surface water sources is mandatory. Disinfection
was also required for public water systems using surface water supplies. The
filtration and disinfection requirements are being proposed as treatment techniques
to protect against exposure to Giardia lamblia, viruses, Legionella, and other
pathogenic organisms. Common filtration methods used for removal of particulates,
destabilized precursor material, and microbial contaminants and applicable
for small water systems include the following options: package conventional
or direct filtration treatment plants; ultrafiltration (membrane or cartridge);
slow sand filtration; and precoat (diatomaceous earth) filtration. Package
and ultrafiltration treatment plants have been known to effectively reduce
precursor material; package plants by coagulation, e.g., alum addition, and
ultrafiltration by size exclusion. Package plants are defined as factory-assembled,
skidmounted units incorporating individual processes similar to conventional
or direct clarification treatment plants. Their compact size, minimal installation
requirements, and ability to operate with little supervision makes them attractive
to small communities. However, the necessity for controlling chemical coagulant
dosage is an inherent disadvantage to small communities with limited resources
for hiring and keeping skilled water treatment plant operators. Large chemical
dosages can also increase the cost of providing drinking water because of the
increased chemical usage and sludge volumes requiring proper handling and disposal.
Ultrafiltration has successfully reduced THM precursors from ground water supplies
in Florida. However, operating pressures up to 100 psi and pretreatment processes
similar to a package plant may be required for water supply sources with low
to moderate color and turbidity levels.
This project designed, constructed and installed a field scale pressure
filter system for the Town of Contoocook, NH. The system was then
fun for seven months to evaluate the success of this technology for
surface water treatment.
Principle Findings and Significance:
The influence of precoat DE size, precoat DE loading or dose, and bodyfeed
DE size and dose on the treatment and operational performance of the pilot
filtration system were evaluated during the study. During these various filtration
trials, the operator took the opportunity to evaluate the filter hardware
and computer software features in terms of operation and maintenance requirements
and system reliability. The results from the completed 12-month study are
summarized below.
Software:
The software system accomplished all primary objectives. The hardware could
use more expansion slots to allow telephone notification capability.
Precoat DE Size: The influent flow rate decreased over time as the
headloss in the filter increased because the DE pilot plant was operated
at constant gravity with no flow controller. The best hydraulic performance
was obtained by the medium grade DE (Celite 503). The 503 grade had
slow headloss development, but did not treat quite as much volume
as the larger 545 grade DE. Visual inspection of the filter coat
by the operator showed uneven filter coating with the 545 grade at
all precoat doses.
The best treatment performance was obtained by the medium grade
DE (503). Initial effluent turbidity levels were similar for all
three grades of DE. However, the larger and smaller grades exhibited
turbidity breakthrough, as shown by rising effluent turbidity levels,
after treating less water than the 503 grade. As expected from previous
studies, no differences between DE grades were observed for NPDOC
removals.
Precoat DE Dose: The optimum precoat dose for both the 503 and the
545 DE grades, as determined by headloss development, was 0.15 lb/
ft2. For all grades of DE tested, 0.15 lb/ ft2 was the optimum dose
for maximum volume of water treated at a minimum terminal headloss.
The best treatment performance was
obtained at the 0.15 lb/ ft2 precoat loading for the 503 and the
545 DE grades. The Hyflo-Super Cel performed best at the 0.10 lb/
ft2 precoat loading. The lighter (0.10 lb/ ft2) and heavier (0.20
lb/ ft2) precoat loading exhibited turbidity breakthrough after treating
less water than the 0.15 lb/ ft2 precoat loading for both the 503
and 545 DE grades. Again, no differences between precoat loading
was observed for NPDOC removals.
Bodyfeed Dose and Size: After determining
the optimum precoat grade and loading, i.e., Celite 503 at 0.15
lb/ ft2 dose, various bodyfeed combinations of DE size and dosage
were tried. All bodyfeed application rates resulted in faster headloss
development than using precoat only. Influent flow rates decreased
more rapidly for all bodyfeed application rates than for precoat only.
The best treatment performance was obtained using only the precoat.
Turbidity removals were better than using only the precoat, at the
lowest bodyfeed application rate with the same size bodyfeed DE as
the precoat. Again, no difference between bodyfeed rates and precoat
were observed for NPDOC removals. Consequently, bodyfeed additions
were not found to be beneficial to optimize filter precoat operational
performance.
Challenge Run: The challenge run was performed on the optimum precoat.
The optimum was determined by the previous trials to be 0.15 lb/
ft2 503 precoat without any bodyfeed. The influent water was spiked
with primary effluent from the town's sewage treatment plant after
the precoat had been applied, and the filter equilibrated for approximately
two hours.
Headloss development occurred rapidly, although the influent flow
rate was lower than in previous trials. Treatment performance, as
measured by effluent turbidity, was slightly better when compared
to previous trials; however, breakthrough occurred much sooner, possibly
due to the significantly higher raw water turbidities observed during
the challenge run.
Results of the bacteria tests were inconclusive, and further study
is necessary before any conclusions about bacterial reductions can
be made.
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