United States Off ice of Water May 1980
Environmental Protection Program Operations (WH-547) 430/9-80-005
Agency Washington DC 20460
Water
Wastewater Irrigation
of Rice
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Technical Report
Wastewater Irrigation of Rice
by
Jack L. Witherow
Land Treatment Task Force
Robert S. Kerr Environment Research Laboratory
Ada, Oklahoma
May 1980
U.S. Environmental Protection Agency
Office of Water Program Operations
Municipal Construction Division
Washington, D.C. 20460
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Disclaimer Statement
This report has been reviewed by the Environmental Protection Agency
md approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Environmental Protection
Agency, nor does mention of trade names of commercial products constitute
endorsement or recommendation for use.
Comment
This bulletin was prepared as one of a series of reports to finish
information on studies and current practices on use of municipal effluents
for crop production. It was prepared in response to many requests for
technical guidance on this topic.
The overall series provides indepth presentations of available
information on topics of major interest and concern related to municipal
wastewater treatment and sludge management. It is a continuing effort to
provide current state-of-the-art information concerning sewage and sludge
processing and disposal/utilization alternatives, costs, transport,
environmental influences, and health factors.
These reports are not a statement of Agency policy or regulatory
requirements. They are published to provide planners, designers,
municipal engineers, environmentalists and others with detailed information
on specific municipal wastewater treatment and sludge management options.
arold P. Cahill, Jr., Director
Municipal Construction Division
Office of Water Program Operations
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WASTEWATER IRRIGATION OF RICE
by
Jack L. Witherow*
Summary
The three areas evaluated in this report are: the potential for
and extent of wastewater reuse in rice production, the resulting food
chain effects, and the cost effectiveness of this reuse.
Rice irrigation occurs in Arkansas, Louisiana, Texas, Missouri,
Mississippi and California and uses 2.8 million acres of land and over 8
million acre feet/year of water. In the counties with large acreage in
rice production, there are over 400 small or medium size communities
having a combined wastewater discharge of about 100,000 acre feet/year.
There are also three metropolitan areas with an estimated combined
discharge of 400,000 acre feet/year. The water requirement for rice
irrigation far exceeds the local wastewater discharges. Many small or
medium size municipalities have a high potential for a land treatment
system, which could reuse wastewater in rice irrigation.
Six cases of municipal wastewater reuse for rice irrigation were
found in the Central Valley of California. These treated municipal
wastewaters constitute up to 75 percent of the waters used to irrigate
rice. Treatment presently consists of primary units and oxidation
ponds. However, these cases of wastewater irrigation of rice have been
ongoing for 30 or more years, and some municipalities had only primary
treatment until recently.
The published literature documented wastewater irrigation of rice
outside of the U.S. and showed a worldwide practice of wastewater rice
irrigation with one or more cases in the countries of Italy, Taiwan,
Japan, China, India and USSR. A case where industrial wastewaters were
used in Japan and another in Taiwan indicate the benefits of organic
matter and the detriment of soluble solids to rice yields, respectively.
A case in USSR, using municipal wastewater which is mostly domestic, had
preapplication treatment similar to that recommended in EPA's Construc-
tion Grants Program Requirements Memorandum (PRM) 79-3. The treated
wastewater applied to the rice paddies had an average BOD,, of 39 mg/1.
*Land Treatment Task Force, Robert S. Kerr Environmental Research
Laboratory, Ada, OK.
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After two days' retention in the paddles, the discharge had a BOD
ranging from 1.5 to 2,0 mg/1 arid toral bacterial counts ranging from 10
to 300/ml.
The potential for introducing a health hazard into man's food chain
is through metal contaminantss biological contaminants, and biocidal
contaminants (toxic chemicals). Of the three, metal contaminants have
resulted in the only known health hazard in wastewater irrigation of
rice. This was a case of untreated industrial wastewater, adding cadmium
to the water used in nearby irrigation of rice.
Many metal contaminants are not significant potential health hazards
because they are generally present in low concentrations, are not readily
taken up by plants, or are not very toxic to man. Several heavy metals
(particularly Cd, Zn, Mo, Ni, Cu) are labelled as posing a potential
health hazard. A compilation of greenhouse and field experiments has
indicated particular circumstance and levels of heavy metals which
should be avoided. For example, to prevent health problems, zinc and
cadmium should be maintained in tha soil at less than 500 mg/kg and 40
mg/kg, respectively. The "Process Design Manual for Land Treatment of
Municipal Wastewaters," (EPA 625/1-77-008), Table 5-4 lists maximum
application of these and other metals "without need for further investi-
gation." The inclusion of industrial wastewaters into the municipal
system is the cause of metal exceeding these maximum values. Thus a
review of the industrial sources, analyses of suspected metals from
these sources, and use of Table 5-4 will prevent this potential health
hazard.
Biological contaminants in food have been extensively studied..
Bryan has compiled a lengthy list of disease outbreaks through foods
which were irrigated with wastewater. Examination of the list shows
that the outbreaks occurred with food eaten raw. Rice, like wheat, is a
cereal crop which is not eaten raw. However, unlike wheat, a part of
the rice harvested is eaten in the grain form. This causes special
concern because of the direct prolonged contact of the rice with the
irrigation wastewater. There are a number of factors which reduce this
potential hazard to the food chain to nonsignificant levels, Pretreatment
and the six to nine month storage of the wastewater greatly reduce the
parasites, bacteria and virus. The hot air drier used to reduce moisture
prior to storage of the grain further reduces any surviving pathogens.
Milling removes the surface of the grain which contacted the wastewater.
Most significant, however, is the necessity of cooking at a boiling
temperature prior to human consumption.
Biocidal contaminant investigations have been made on the common
toxic organic chemicals used in rice production. The concentrations
required to increase the uptake or residual on the unhulled rice grain
are two to four orders of magnitude greater than the concentration of
these types of compounds in domestic wastewater. The placement of toxic
persistent organics in man's food chain will not occur via irrigation of
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rice with domestic wastewatet. However, an industrial discharge with
high levels of biocidai contaminants would need i.c, be evaluated prior to
reuse in the irrigation of rice.
A cost comparison of three land treatment schemes was made to
determine if wastewater irrigation of rice, is cost effective. The land
and capital costs for nine months of wastewater storage for rice irriga-
tion was compared with two months of storage plus forage irrigation and
with one month of storage plus an overland flow process. The overland
flow system is expected to have less land and capital costs than nine
months of storage. The forage irrigation system will have capital costs
similar to nine months of storage. The costs of land treatment systems
are very site specific, but these comparisons show that an overland flow
or a forage irrigation system may be cost effective and should be fully
evaluated. Controlling factors which must be added to these cost
comparisons are: site characteristics, differences in transportation
distances, crop revenues, operation and maintenance, and purchase of the
water or storage by the rice farmer.
Recommendations
Wastewater irrigation of rice should be viewed as having the same
health hazards as wastewatar irrigation of wheat or other controlled
agricultural food crops which are not eaten raw. (PKM 79-3 recommends
prior to reuse: "Biological treatment by lagoons or inplant processes
plus control of fecal coliform counts to less than 1,000 MPN/100 ml.")
The industrial discharges to the municipal systems should be inven-
toried and analyses made of heavy metals and persistent organics that
are suspected of being present and of being a health hazard to man. If
concentrations of these materials are less than those maximum values in
the "Process Design Manual for Land Treatment of Municipal Wastewater"
or less than the toleranceresiduals levels of the commonly-used registered
biocides, the treated wastewater should be acceptable for reuse in rice
irrigation. If the concentrations are greater, several courses of
action should be considered. Among these are denying approval for reuse
on rice irrigation, requiring pretreatment to reduce the concentrations
to acceptable values, or approving reuse on the condition that annual
monitoring of the soil and crop for heavy metal and persistent toxic
organic show concentrations below recommended values.
Monitoring and reporting requirements should be established to
determine new industrial discharges to the municipal system that contain
heavy metals or persistent toxic organics, and to determine the environ-
mental quality of water discharged from the storage lagoons and the rice
paddies to both surface and ground water sources.
Potential for and Extent of Reuse
The potential for reuse of municipal wastewater for irrigation of
rice is dependent upon the acreage of rice grown and the amount of local
wastewater. Annual rice production of 12 billion pounds in the United
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States is derived from about 2.8 million acres. The producing states
are Louisiana, Arkansas, Texas, California, Mississippi and Missouri.
The breakdown of the 1975 production by acres, pounds, and dollar value
is shown in Table 1.
TABLE 1. 1975 RICE PRODUCTION (1)
States
Acres
Cwt.
Dollars
AR
CA
LA
MS
MO
TX
TOTALS
882
525
658
171
18
548
2,818
40SG53
30,088
25 , 064
6,665
758
24,996
126,624
322,427
225,660
177,954
54,320
6,102
224,964
1,011,427
(1) in thousands
To establish feasibility, the extent of existing wastewater irrigation
of rice was determined. However, the United States has only 1 percent
of the acreage used for rice cultivation throughout the world, and the
practice of irrigating rice with wastewater was found to be more common
in foreign countries.
Arkansas - Rice is produced in 35 counties in Arkansas, mostly in
the eastern half of the state. Counties having the largest acreage
ranked in order are: Arkansas, Prairie, Lonoke, Poinsett, and Cross.
In counties with substantial rice production, there are several cities
and numerous small towns. Each county has about a dozen small towns
with less than 1,000 population, and two communities with populations
between 1,000 and 5,000. The cities of Pine Bluff, Stuttgard, Searcy,
Jonesboro, and Forest City are located in heavy rice-producing counties.
These cities with populations over 10,000 have sufficient wastewater to
irrigate several hundred acres of rice. A consultant for Searcy has
made a preliminary investigation and proposed a scheme to use that
city's wastewater to irrigate part of 10,000 acres of nearby rice production.
An ample supply of irrigation water is necessary for successful
rice production. About 33 inches of water are required to produce a
rice crop in eastern Arkansas. Twenty to 24 inches of this amount will
have to be supplied by irrigation. The amount of irrigation water
needed will vary depending upon the amount and distribution of rainfall,
humidity, temperature, evaporation, type of soil, and water management.
This last item, water management, can overshadow the others. USDA
personnel in several states have stated common practice is to apply
between seven and ten feet of water, consume about three feet, and
discharge the rest.
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Texas - The principal Texas rice-growing area is in 19 counties
making up the physiographic area of the gulf coast prairie. The rice
production in Texas is presently between five and six hundred thousand
acre. The Texas Water Development Board has predicted that by 2020, the
acreage in rice will have doubled in Texas. The gulf coast rice belt is
highly industrialized and populated. The area includes Houston, the
largest city in the state, and over 50 other smaller communities. Water
usage in rice production exceeds the municipal wastewater discharged in
this area.
Louisiana - There are two principal rice-growing areas in Louisiana.
These consist of seven parishes (counties) in the southwest and six
parishes in northeast parts of the state. The southwest parishes with
the largest acreage in rice production are Jefferson Davis, Acadia and
Vermilion. There are about 10 small communities in each of these three
parishes. The only large municipalities, Lake Charles and Lafayette,
are in adjacent parishes, and transport distance will likely prevent
wastewater irrigation of rice. In the northeast area, Morehouse and
Richland are the parishes with the largest acreage in rice production.
In each parish, there are less than 10 small communities. Monroe, the
only city in northeast Louisiana, is in Quachita parish, and rice is
grown in this parish. The opportunity for irrigation of rice with
municipal wastewater in Louisiana will be mainly small communities and
Monroe. Between 30 and 36 inches of water are consumed to produce rice
in Louisiana. Thus, each acre of rice irrigated will require a sewered
population of 35 to 40 people.
Mississippi - The rice growing area is in the west central portion
of the state. Most of the rice acreage is in Bolivar, Washington,
Sunflower, LeFlore, Tunica, Coahoma, Humphrey and Sharkey counties.
This acreage is concentrated in the flood plains of the Mississippi,
Sunflower and Tallahatchie rivers. These counties contain 80 small
communities and the larger municipalities of Greenville, Greenwood and
Clarksdale.
Missouri - Of the six rice-producing states, Missouri has the
smallest acreage in rice cultivation. Rice is grown in the southeast
part of Missouri. The principal rice-growing counties are Butler,
Ripley, and Stoddard. In these counties, Popular Bluff, with c< population
of about 17,000, is the only large community, but there are also 40
small communities. The opportunities for irrigation of rice w'th municipal
wastewater will be limited to a few communities with nearby rice paddies.
California - California has wastewater reclamation criteria for
irrigation of food crops. The required levels of preapplication treatment
would in almost all cases produce an effluent suitable for discharge.
However, exceptions are made to the required quality of the reclaimed
water when it is to be used to irrigate a food crop which must undergo
extensive commercial, physical or chemical processing sufficient to
destroy pathogenic agents before it is suitable for human consumption.
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Wastewater irrigation of rice is being practiced in a limited manner in
California.
In California, water consumption is about 36 inches per year for
rice production. Application of the seven to nine feet per year is
practiced with most going to the drainage system. Irrigated agriculture
in the Central Valley is highly organized through irrigation districts
and water rights. The rice-growing areas are loca.ted in 16 counties.
Most of the acreage is in Butte, Colusa, Fresno, Glen, Sacramento,
Sutler, Yolo and Yuba, All of chese counties except Fresno are locaced
in the northern half of the Central Valley. There are between 13 and 25
small communities in each of these northern counties. In the rice-
growing areas, there are three communities with populations between
40,000 and 60,000, but Fresno and Sacramento are the only major cities.
Extent of Reuse in tag._jjJLS_1 - Water reuse is common and highly
encouraged by"the state of California. Irrigation water transport and
drainage canals are publicly owned, Wastewater from several segments of
society are discharged to these public-funded canals. The State is not
aware of rice paddies wholly irrigated by municipal wastewater; however,
there are a number of sioall towns in the northern part of the Central
Valley that for 30 years or more ha\re been discharging their wastewater
into a drainage system. All of these small towns now have primary
treatment followed by oxidation ponds. This wastewater is used for the
irrigation of rice.
Examples of irrigation of rice with wastewater provided by California's
Central Valley 'water Quality Board follow:
(1) The town of Colusa discharges about 0.5 mgd into Powell Slough.
The flow in the slough is half treated sewage and half irrigation
return flow. A farmer has been using this water for irrigation
of rice for a number of years. Until just recently, the
sewage received only primary treatment. The farmer recently
initiated a suit against the City to retain use of their
wastewater for rice irrigation.
(2) The town of Willows also discharges 0.5 mgd into a public drain
which constitutes ha]f of the flow in the drain. This
is used for irrigation of rice.
(3) The town of Williams dicharges about 0.5 mgd into Salt Creek
which represents up to 75 percent of its flow. This water is
used to irrigate rice and other crops.
(4) The small town of Biggs discharges their wastewater to a
drain. The discharge is about 10 percent of the flow anc the
water is diverted to irrigate rice and other crops.
(5) Some of the wastewater from the town of Live Oak is used in a
similar manner for rice irrigation.
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(6) The town of Maxwell discharges its wastewater into Stone
Corral Creek, which flows into the Glenn-Calusa irrigation
district's irrigation canal. The municipal wastewater, which
is about 10 percent of the flow, is used to irrigate rice.
This irrigation district included 121,170 acres of cropland
in 1978, 3/4 of which were devoted to rice production.
Both the Regional Water Quality Board and State Health Department
are aware of the uses of treated municipal wastewater for rice irrigation
and do not feel a change is necessary, as problems have not occurred
from these long standing practices.
In Arkansas, Texas, and Louisiana, rice is a major cash crop, and
they all have experimental stations which specialize in research on rice
production. These experimental stations are located at Stuttgart, Arkansas;
Beaumont, Texas; and Crawley, Louisiana. All three stations are part of
the agricultural research program directed from the states' land grant
colleges. Contact was made with these stations, but information was not
available on wastewater irrigation of rice in these states.
Foreign - A literature search was made in June, 1979 by EPA's
library services. This computer-based search of articles on rice irrigation
with wastewater, sewage, or sludge located eight articles.
This limited list shows rice irrigation with wastewater has been
practiced in Italy, Taiwan, Japan, India, and USSR since 1969. The
small number of references is probably due to the fact that computer-
based bibliographies were begun in the last decade and seldom contain
literature published prior to 1960. Outside of establishing that rice
irrigation with wastewater is practiced around the world, several of
these articles are germane to conditions that can be expected in rice-
growing areas in this country. Two of the articles relate the increase
or decrease in rice yields to various constituents in industrial wastewater.
Minami showed that yields increased with increasing BOD of the
water up to 50 ppm (COD 200 ppm), but above this level yields decrease.
High-level BOD water produced reducing conditions in the soil and promoted
the leaching of inorganic elements (Fe, Ca, Mg) with an associated
increase in acidity. The wastewater was pulp mill sulphite liquor that
had been neutralized by dilution with river water. Huang found rice
yield loss as high as 89 percent when wastewaters from a paper *nill or
an acetyl chloride plant were used as a part of the irrigation water.
The results of analysis indicate that both industrial wastewaters and
the polluted irrigation waters were not acceptable for irrigation purposes
because of high soluble solids and salts.
The most significant article is by Koltypin, who describee the pre-
application treatment and use of sewage in rice paddies in the USSR.
The wastewater was from Dushanbe and consisted of 60-65 percent domestic
sewage and 35-40 percent industrial effluent. The wastewater was
treated in four ponds in series, used in eight to twelve rice paddies in
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series, and discharged. The first pond served as a settling tank with
an area of. 2 ha (4.4 acres), a depth of 1.5 m (5 ft) and a detention of
10 hours. The subsequent biological ponds had areas of 4 to 4.5 ha (10
to 11 acres) and a depttj of 0.6 m (2 ft). The quantity of wastewater
discharged was 58,200 m'/day (15MGD). The detention time in the three
biological ponds was 33 hours, and the BOD,- loading was 672 kg/ha/day
(600 Ib/acre/day). The rice paddies had a total area of 25 ha (62
acres) with a mean water depth of 25 cm (10 inches). Their total water
capacity was-62,500 m ; the inflow was 52,200 m /day and the discharge
was 30,000 m /day. Thus the detention was about two days.
A part of the analytical results are reported in Table 2.
TABLE 2. REMOVALS IN LAGOONS AND RICE PADDIES
Items
BOD5 (mg/1)
Dissolved oxygen (mg/1)
Helminth eggs (per liter)
Ammonia (mg/1)
Total bacterial (counts/ml)
Raw Waste
Ave*
120
0
23
—
—
Pond Effluent Paddy
Ave*
39
3
0
—
—
Min
1.5
8.5
0
0.5
10
Effluent
Max
2.0
12.0
0
1.0
300
*Mean value from 26 determinations.
The aquatic organisms in the paddies included algae, diatoms,
dragonfly larvae, carp, and mosquito fish. The system depends upon both
the ponds and rice paddies for treatment. The effluent from the paddies
is highly treated.
Koltypin concluded "Extensive utilization of paddy fields for the
decontamination of sewage is possible in the rice-cultivating regions of
the USSR. In the vicinity of cities, with industrial-type sewage treatment
installations already in operation or under construction, paddy fields
may be used for the additional purification of sewage after leaving the
aeration tanks and biofilters. In many cases, with small volumes of
effluents from enterprises, rest homes, pioneer camps, and other similar
sources, paddy fields may be combined with biological ponds. Finally,
paddy fields may become an essential component of sewage farms in the
zone of rice cultivation in the south of the USSR."
These treatment ponds are more heavily loaded and have shorter
detention than those used in the U.S. In the U.S. where the wastewater
is to be used in controlled agriculture fields and on human food crops
not eaten raw (ie. rice), PRM 79-3 recommends preapplication treatment
by either biological lagoons or inplant processes plus control of fecal
coliforms to less than 1000 MPN/100 ml.
Metal Contaminants - The food chain involves acquisition of the
metal by rice plant roots, transport into the rice grain, and then
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consumption by man. Many metals are not a significant potential hazard
either because they are generally present in low concentrations, are not
readily taken up by plants under normal conditions, or are not very
toxic to plants and/or animals. Several metals (particularly Cd, Zn,
Mo, Ni, Cu) are labeled as posing a potential serious hazard under
certain circumstances.
Except for certain accumulation species, plants are excellent
biological barriers. This is notably true for nickel, copper, and lead.
Molybdenum is an exception to the plant barrier rule, but only ruminants
that consume forages can be affected. Zinc can be transferred to foliar
tissue such as spinach and to the edible tissues of other plants such as
tomato, peas, and potato. Soil levels of zinc in excess of 500 mg/kg
may cause, at least, a decline in forage quality through lower palatability
and at worst some overt toxicity symptoms. Humans are probably protected
from food-chain transfer toxicity because their diet also includes
fruits, grains, and animal meats. In all cases, zinc transferred from
substrates high in zinc is much lower in these tissues than in foliar
tissues of plants.
Cadmium is currently the element of greatest concern as a food
chain hazard to humans. The widely publicized Itai-Itai disease in
Japan is attributed to cadmium introduced into the Jintsu River from
mining activities which was transferred to man through several sources,
including irrigated rice. The World Health Organization has recomriended
a safe value of 400 to 500 ug/week of cadmium. The base level average
dietary intake of cadmium has been reported to range from 175 to 525
>ig/week for an adult consuming 1.5 kg/day of food. Cadmium intake of the
people affected by Itai-Itai disease may have been 4200 to 7000 ug/week.
The limit recommended by the Japanese investigations as the maximum
permissible concentration was 1.0 ug Cd/g of rice grain. Their results
associated a concentration of 15.5 ;ag Cd/g extracted from the soil with
0.1 N HC1 with excessive levels of Cd in rice grain.
Two important foodstuffs, rice and wheat, are able to take up
considerable quantities of Cadmium from soils. Kobayashi et al. added
cadmium oxide to soil in pots where rice and wheat were growing. The
results are in Table 3. The wheat grain accumulated more cadmium than
did rice. Concentrations above 10 ug/g (.001 percent) in soil reduced
the yield of both rice and wheat. However, concentration of 100 pg/g in
the soil did not result in the rice grain's reaching the maximum level
of 1.0 ^ig Cd/g recommended by the Japanese.
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TABLE 3. UPTAKE OF CADMIUM BY RICE PLANT AND WHEAT AS WELL AS YIELD
Addition
of Cd
to Soil
(% of CdO)
0
0.001
0.003
0.01
0.03
0.1
0.3
0.6
1.0
Yield
(%)
100
100
92
92
93
69
32
19
1
Rice
Polished
Cd (ug/g)
0.16
0.28
0.40
0.78
1.37
1.62
1.94
1.73
4.98*
Bran
Cd (ug/g)
0.59
0.79
0.84
1.60
2.68
2.94
3.19
3.94
Yield
(%)
100
106
72
16
13
3
3
2
1
Wheat
Whole grain
Cd (tig/g)
0.44
8.27
15.5
29.9
41.4
60.7
48.6
90.8
139.0
From Kobayashi et al., 1970.
Bingham et al., in a greenhouse investigation conducted in California
in 1975, showed the uptake of cadmium by rice grain increased with
increased amount in the soil, but was much less under flooded than non-
flooded cultures. Under flood and non-flood conditions, rice grain with
concentrations in excess of 1.0 ^ig Cd/g was produced when DTPA-TEA soil
extractable Cd was 40 and 15 pg/g, respectively. Thus, with flood
culture rice, design calculations should be required showing an accumulation
of cadmium in the soil of less than 40 ug/g. Naturally-occurring levels
of Cd in soil average 0.06 ug/g and range from 0.01 to 5. ug/g (extracted
with 0.1N HC1).
Biological Contaminants - Enteric pathogens survive some stages and
sometimes the entire process of wastewater treatment. Viable pathogens
are therefore applied to the land and the crop in the process of irrigation
with wastewater. After application, the pathogens must survive long
enough to be present when the crops are harvested.
The greatest health concern is with low-growing crops such as
vegetables which have a greater chance of contamination and are often
eaten raw. Outbreaks of disease have occurred from foods contaminated
by wastewater. Bryan has compiled a lengthy list which shows outbreaks
occurred with food eaten raw.
Prior to and during reuse of wastewater for rice irrigation, biological
pathogens will die due to long exposure to unfavorable environmental
conditions in the preapplication treatment facilities, storage ponds and
rice paddies. The most common treatment facilities will be lagoons with
about a month detention. Storage ponds will have 7 to 9 months detention,
and the paddies will remain flooded for 3 to 5 months. Reduced water
levels in the storage ponds and discharges from the paddies during the
growing season will reduce these detention times.
10
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The removal of both virus and bacteria in ponds have been shown to
be time and temperature dependent. Sagik, et al., have shown the
reduction of virus is quite rapid at 20 C as is illustrated in Figure
1., which is results from research in Texas. Similar results for fecal
coliforms have been found in wastewater ponds, and Bowles has developed
the following equation describing the die-away function.
In Ci/Cf . K 8(T 20)
where: t = Actual detention time in days
Ci = Entering counts/100 ml
Cf = Final counts/100 ml
K = 0.5 in warm months
= 0.03 in cold months
9 = 1.072
T = liquid temperature (°C)
Short circuiting occurs in almost every pond. The actual detention
time was found to range from 25 to 89% of the design time with a geometric
mean of 46%. Using Bowies' equation, about 18 days is required to reach
the recommended fecal coliform count of 1000/100 ml at 20 C. This is
similar to the time required for virus removal shown in Figure 1.
Studies have been made on the viability of various pathogenic
organism on crops irrigated with wastewater. The values in Table 4 show
the viability of such organisms varies from less than a day to 49 days.
TABLE 4. SURVIVAL OF SELECTED PATHOGENS ON VEGETATION
Organism Media Survival Times (days)
Salmonella
Salmonella
Tubercle bacilli
Entamoeba histolytica cysts
Enteroviruses
Ascaris Ova
vegetables
grass or clover
grass
vegetables
vegetables
vegetables
3-49
12->42
10-49
-------
100
0
20 40 60 80
Time (days)
Figure 1. Virus Survival in Ponds
100 120
lla
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increased 65 percent between 1950 and 1970. Much of this increase in
consumption is in breakfast cereals or specialty prepared food. These
uses require high temperature process t t'> Tvhich will destroy biological
pathogens. Direct use of rice v.raia. requires cooking which is universally
done with water at boiling temperature. The sequential and additive
effects of die off in storage, neat drying, and finally cooking of the
product provide a very effective barrier for biological contaminants.
Biocida1 _CjHitamio?nLs_ -- Biocidal contaminants can be generally
described as chlorinated hydrocarbons, rrsenated hydrocarbons, urgano-
nitrogen pesticides, organophosphorus pesticides, herbicides and soil
sterilants. Some of the most recognized compounds are DDT, Dieldrin,
2,4-D, Parathion and PCS. The concentration of all of chese in wastewater
is negligible compared to other sources and are far below levels that
will cause scute health effects.
The major concern in placing th^se compounds in man's food chain
has been in waste discharges to drinking water sources and surface
contact on foods. Bej.-.use of Ch^ir persistence the possibility of
increased uptake by rir-i with increased concentrations in the irrigation
water has been studied. An unpublished paper by Yin-hsiao indicates the
degree of uptake in rice of a heavy metal, arsenic, end a persistent
organic compound, phenol. (The major biocides used in rice culture in
the U.S. are phenolic compounds, ie. Propanil, Carbofuron and Carbaryl.)
In experimental plots, each with an area of 0.66 m and 80 cm deep, rice
was irrigated with wastex^ater containing 0, 0.5, 50, 100, 250, and 500
ppm of phenol and in separate plots rice was irrigated with wastewater
containing 0, 5, 10, 20, and 50 ppm of Arsenic. The uptake by the rice
is shown in Figures 2 and 3. These figures show the uptake in the root
and in the stem and leaf is much greater than in the unhulled rice.
Concentration of phenol and arsenic in the unhulled rice is the same
with concentrations of 0 and 50 ppm of phenol and 0 and 10 ppm of arsenic
in the irrigation water. Yiu-hsiao concludes "The effect of the phenolic
compounds on the crops and their accumulation in the plant is influenced
by various factors (temperature, humusv etc.), especially the concentration
of phenolic in the. irrigated sewage. Under the field condition^, wheat,
rice, and corn irrigated with a low concentration (under 1 ppm) of
sewage containing phenolic compounds show a good growth and development.
Their phenolic content do^rm't show a distinct difference in comparison
with those irrigated with clean water. But under the experimental
conditions, if the phenolic concentration increases, the level of the
phenolic content and its accumulation are somewhat different. lien the
concentration is 50 ppm, both In soil and water culture, the phenol
promotes the growth. When the concentration increases further, however,
the result turns to the opposite. Vhen concentrations are over 50 ppm
in soil culture, the phenolic content in the crops may be increased; as
the concentration raises up to 500 ppm, the crops growth is inhibited....
"The effect of arsenic on the crops and its accumulation is obviously
influenced by the arsenic concentration of the irrigated sewage.... At
low concentration (1 ppm~> arsenic promotes the growth of wheat and
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e
a,
a
1000
900 •
800 •
700 -
600 .
500 •
o
-------
Stem and Leaf
Unhulled Rice
C
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rice. However, as the concentration rises up to 5 and 10 ppm, the
growth of the wheat and rice are inhibited respectively, and the arsenic
accumulation in the crops became more evident. As the concentration
rose to 50 ppm, the growth of wheat and rice are heavily injured, and
the arsenic content in plants increases."
In the U.S. The four common biocides used in rice culture are
listed in Table 5 along with the recommended applications and the tolerances
for residue on the rice grain. Brown has investigated these biocides
and developed management guidelines for their use.
TABLE 5. BIOCIDES USED IN CULTURE OF RICE
Recommended Application Tolerance on grain
Herbicides (Ib/acre)
Propanil
Molinate
Carbofuran
Carbaryl
3.0
3.0
0.5
1.0
2.0
0.1
0.2
5.0
The tolerance limits on rice are those found as residues when the
recommended applications are followed. The residue is measured on a
ground sample of the unhulled rice and includes the residue on the hull,
bran, and grain. The grain that is eaten will contain a small part of
the total residue that is measured.
Sokklov, et al., studied the behavior of several biocides in rice
irrigation systems. He measured the amount translocated to the soil,
rice plants and irrigation waters. Using an application of 14 kg/ha
(12.5 Ib/acre) of propanil, he found different amounts of the biocide in
different years. Sixteen days after the applications, the rice plants
contained 3% in 1972 and nearly 15% in 1973 of the initial amount of
propanil applied. The concentration of propanil and its metabolite
(3,4-DCA) was 25 ug/plant or less on the sixteenth day and decreased to
zero in two to three months. This study shows the small amount of
translocation to the whole plant with an application rate of four times
that recommended in the U.S.
Jolley investigated the effects of chlorination on organic constituents
in effluents from domestic sanitary sewage treatment plants. He found
32 stable organic constituents in effluents from domestic sanitary
primary sewage treatment plants. Twenty-three were quantified at 2 to
190 ug/1 levels. Phenol, at 6 ug/1, was the only compound found that is
on the priority pollutants list. (This list contains those organic
compounds suspected of being serious health hazards.) Nine stable
organic constituents were identified in the effluents from domestic
sanitary secondary sewage treatment plants. Eight of these were quantified
at 5 to 90 fig/1 levels, but none are on the priority pollutant list.
After chlorinating to a 1 mg/1 chlorine residual, seventeen chlorine-
13
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containing stable organic compounds were present in the effluent from a
secondary plant treating domestic sanitary sewage, These seventeen
compounds were quantified at the 0.5 to 4.3 yug/1 levels. Two of the 17
compounds are on the priority pollutant list. These were 2-chlorophenol
at 1.7 jag/1 and 4-chloro-3-methyl phenol at 1.5 ug/1.
Jolley's work indicates the extremely low level of stable organic
chemicals that can be expected in domestic wastewaters use in irrigation.
Phenol and two chlorinated byproducts were the only compounds found
which are considered to be a potential health hazard. The concentrations
of these phenolic compounds were four orders of magnitude less than the
level Yin-hsiao found causing an increase in the phenol content of
unhulled rice grain and two orders of magnitude less than the tolerance
limits for residual of several phenolic-base pesticides used in rice
production. An increase of persistent toxic organic in man's food chain
will not occur via irrigation of rice with domestic wastewater; however,
the inclusion of industrial wastewater with biocidal contaminants above
the tolerance level would need to be evaluated prior to reuse in the
irrigation of rice.
Economic Feasibility
Storage - Wastewater irrigation of rice will require storage of the
wastewater during non-irrigation periods. The amount of storage is a
controlling economic factor.
The length of time to grow rice is dependent upon the variety
planted. Very short season varieties require 120 days, while short
season or midseason require 140 and 155 days, respectively. Rice may be
flooded when rice seedlings are 4 to 6 inches tall, which will be 3 to 4
weeks after planting. Water is added through the growing season to
maintain the depth of water between 4 and 6 inches. The paddy is usually
drained about two weeks prior to harvest to allow the field to dry and
accommodate mechanical harvesting equipment. This sequence of events
requires use of large quantities of irrigation water over a three to
four month period. In Arkansas, Mississippi, Tennessee, and Missouri,
storage of 8 to 9 months would be necessary for growth of this single
crop. In the southern parts of Louisiana and Texas, a second crop of
rice can be produced from the stubble remaining after the first cutting.
This "stubble" crop will consume another 12 inches of water and extend
the water use period from 3 months to about 5% months. Consequently, in
these areas with longer growing seasons, less storage is needed.
The decline in the supply of underground water in the Grand Prairie
area in Arkansas has stimulated interest in reservoirs as a means of
utilizing surface water for rice irrigation. A survey made in 1958 by
the Arkansas Agricultural Experimental Station shows 106 reservoirs had
been constructed by farmers to store water for rice irrigation. The
economic evaluation part of the survey showed that the larger reservoirs
(80 to 160 acre) had less per acre cost than irrigation from wells, but
that smaller reservoirs (20 to 40 acre)had costs of 10 to 35 percent
higher than the costs of irrigation from wells. The major cost factor
14
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in reservoir storage was land. When waste land was available, cost
savings were obtained with 20 to 40 acre reservoirs.
When using water from reservoirs, farmers usually drained their
fields only once, compared with one to three times when well water was
used. This drainage of the field fewer times and more rapid flooding
when water was applied resulted in farmers with reservoirs using less
labor, about 2.5 hours per acre, in irrigating rice.
Comparison of Alternative Land Treatment Systems - In order to
determine the opportunity of wastewater irrigation of rice being cost
effective, a series of calculations were made to compare the relative
costs of rice irrigation, forage crop irrigation, and overland flow.
Generalized design conditions were necessarily assumed to enable such
comparisons. Since land treatment costs are very site-specific, the
results can only suggest what alternatives should be fully evaluated in
a facility plan.
The three comparison incorporated: (1) identical primary treatment,
(2) different amount of storage, (3) identical transport (pipeline and
pumping) cost, (4) different periods and rates of wastewater application,
and (5) municipally owned storage, overland flow and forage irrigation
sites but privately owned rice paddies.
Primary treatment was included to reduce solids for odor and
operational reasons and to reduce pathogens for health reasons. Even
though EPA will accept a minimum of comminution and screening for overland
flow systems, more extensive primary systems, such as the aerated lagoon,
are considered necessary by Louisiana and some other states. However,
assuming the primary treatment costs to be the same is a disadvantage to
the economics of the overland flow system.
The storage costs were calculated for nine months of detention for
rice irrigation, two months for forage irrigation, and one month for
overland flow. These storage periods for forage irrigation and overland
flow are one month longer than minimum recommended by EPA for the rice
producing areas. This month was added as a safeguard against infrequent
operation for small treatment plants but is an economic disadvantage to
both forage irrigation and overland flow systems. Because rice is grown
in relatively impermeable soils on flat terrain, unlined storage lagoons
and flood irrigation techniques were assumed for the three systems.
Outside of California, the rice growing areas in the U.S. have more
annual precipitation than potential evapotransporation, and in these
areas hydraulic loading based on soil permeability rather than nitrogen
loadings is the limiting constraint in design of an irrigation system.
The acreage calculations for forage irrigation are based on one inch/week
over ten months of the year. The acreages for overland flow are based
on an application of eight inches/week over 11 months of the year. The
land values in Table 6 include 25% extra for fences, roads, and buffer
zones.
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An inventory showed three predominant sizes of communities in
counties with large acreage in rice production. In accord with the
inventory, calculations were made for populations of 1000, 4000, and
12,000.
Storage costs were determined using EPA's report, 430/9-75-003,
"Costs of Wastewater Treatment by Land Application." The cost curves
used are based on EPA Sewer Construction Cost Index of 194.2 for February,
1973. The costs were updated to the April, 1979 Sewer Construction Cost
Index of 344.9. The storage costs include reservoir construction and
embankment protection but not lining or land. The land areas for storage
are calculated on: (1) 5 ft water depth in reservoir less than 10
million gallons, (2) 12 ft water depth in reservoirs above 10 million
gallons, and (3) dike configuration as specified in the above report.
The design factors which highly influence the economics of these
land treatment systems are storage volume and land areas for the application
site and the storage lagoons, A tabulation of these items are shown in
Table 6-
TABLE 6._ COMPARISON OF THREE LAND TREATMENT SYSTEMS
. Populations
Items 1000 4000 12000
Million gallons/year 25 100 300
Capital Cost of Storage ($1,000)
9 months 71 248 604
2 months 51 87 195
1 month 37 73 124
Land for Storage (Acres)
9 months 7.2 23.8 65.5
2 months 3.8 6.5 16.5
1 month 2.5 6.9 9.1
Land for Application (Acres)
Forage Irrigation @ l"/wk 25 100 300
Overland Flow @ 8"/wk 3 12 37
Differential Acres
(Forage Irrigation area & storage -
9 month storage)
Differential storage costs (9-2 months)
($1,000)
Differential storage cost per
differential acres ($l,000/acre)
7.6
20
0.9
27.7
161
1.9
81.
409
1.6
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The capital costs for storage are shown for three population levels
and three storage periods. The land required for these nine storage
ponds is tabulated as is the land for forage irrigation and overland
flow application sites.
These economic evaluations of storage and land requirements for
rice irrigation, forage irrigation, and overland flow indicate the
overland flow system will have the least capital costs. The economic
comparison shows similar capital costs between a municipally-owned
storage and forage irrigation system and a system with privately-owr5d
rice irrigation and municipal storage facilities.
The overland flow system is likely to have considerable econond c
advantage over rice irrigation with wastewater. The land requirements
for one month of storage plus the application area is less than the land
needed for nine months of storage for rice irrigation. Nine-month
storage is two to five times more costly than one month. This differential
in capital cost for storage is equal to about $12,000/acre to shape and
plant the land and provide an overland flow distribution system. Use of
an overland system will also depend upon permit limitations, soil
characteristics, slope of the land, and transport distances. These are
all site specific and cannot be evaluated in these calculations.
Where an overland flow system is not feasible, forage irrigation
will be economically competitive to rice irrigation. In the rice-
growing areas, it is likely that forage irrigation will be done on
municipal purchased land. Forage irrigation can be managed to minimize
disposal cost without damage to the environment, but the crop selection
may not maximize the cash returns from the land.
The differential in land requirements needed for forage irrigation
(areas for application plus 2 months of storage) minus the land needed
for nine months of storage with rice irrigation are shown in Table 6.
The differential in cost for 9 months over 2 months of storage are also
shown. These differentials show the cost for additional storage needed
for rice irrigation is equal to between $900 and $1,900 per acre of
additional land needed for forage irrigation. These amounts are sufficient
to purchase land in most ricegrowing counties. There are several site-
specific factors which must be included in this comparison prior to
concluding that forage irrigation will be the cost-effective system.
The major ones are purchase of the water or storage by the rice farmer,
forage crop revenues, operating, and maintenance costs and differences
in transportation distances.
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