Water Reuse for Irrigation
Barney
Turf Grass
Barney P. Popkin, Water Resources & Environmental Management
Consultant, RG, REA, EFG, ACHMM, CPSSc
bppo...@yahoo.com
February 23, 2005
"All models are wrong, but some are useful." - G.E.P. Box (1979),
Robustness in Statistics
This review is based solely on my experience and education (only, as
you would say in India), and is not presented to represent the opinion
of any of my clients, colleagues, friends, or employees. Much progress
has been made since I completed my humble M.S. University of Arizona
thesis on effect of soil and grass treatment on Tucson (Arizona) urban
runoff in 1973, contributed to a USEPA land application of municipal
wastewater manual in 1976 for Metcalf & Eddy, established a Christmas
Tree Farm using septic pit effluent for the YMCA Oracle Camp (Arizona)
in the late 1970s for the Arizona Water Resources Research Center, and
visited or reviewed wastewater treatment facilities in Aqaba, Asmara
(Eritrea), Bangkok, Batam (BARELANG, Indonesia), Kathmandu, Luxor
(Egypt), Puket (Thailand), Taiwan; Guadalajara, Juarez, Matamores,
Mazatlan, Nogales, Puerta Vallarta, Puerto Penasco, San Carlos and
Tiajuana in Mexico; Boston, Blue Plains (Washington, DC), Houston, Long
Island (New York City), Madison and Milwaukee (Wisconsin); Flushing
Meadows (Phoenix), Palo Verde Nuclear Power Plant (Buckeye, near
Phoenix, a unique plant cooled by treated wastewater from metropolitan
Phoenix), Patagonia-Sonoita, Phoenix and Tucson in Arizona; and
Gilroy-Morgan Hill, Hyperion (Los Angeles), Monterey, Mountain View,
Palo Alto, Oakland, San Diego, San Jose, San Francisco, and Santee
(California). In a fresh-water resource shrinking world with rapidly
growing fresh water demand and poor water-demand management, much
modern interest returns to the ancient practice from Asia and the
Middle East of wastewater reuse, I note. Wastewater reuse is rapidly
growing worldwide and has numerous obvious benefits, though difficult
to quantify. Practitioners worry that many reuse facilities are
burdened with inadequately treated wastewater, typically from lagoons
receiving raw sewage loads way beyond their design capacity, which
unfortunately produces a nearly raw wastewater source for reuse,
typically irrigation, often raising health and liability concerns and
limiting export potential of resulting crops. Also noteworthy, the
organic matter, oxygen demand, suspended solids, and bacteriological
loads in municipal wastewater are extremely high from low-water use
areas like Amman (Jordan) where otherwise contributing gray water from
showers, baths, sinks, dish and clothes washers as well as local runoff
are more typically efficiently diverted by water uses for onsite
landscape, house plant watering, and car washing; these high loads make
wastewater treatment more challenging than otherwise.
CRC Press's 2005 Water Reuse for Irrigation: Agriculture, Landscapes,
and Turf Grass, edited by the talented and insightful Valentina
Lazarova and Akiça Bahri acknowledges that water reuse programs face
technical, economic, and regulatory challenges related to
environmental, agronomic, and health impacts of recycling of reclaimed
water. It provides guidelines for successful planning and operation of
reuse project, with information, analysis, and experience for
agriculture and landscape irrigation, bridging the gap between science
and economic, institutional, and liability issues. With examples from
El Mezquital (Mexico), Costa Brava (Spain), and Monterey County (U.S),
it provides best practices and examines recent concerns on groundwater,
plants, and public health. The book is rich in tables, flow charts,
maps, photographs, nomographs, and trilinear and matrix diagrams,
correlation plots, histograms, and formulas. Chapters include
Challenges of Sustainability, Water Quality, Guidelines and
Regulations, Health Codes, Successful Agronomy, Codes for Landscapes
and Golf Courses, Wastewater Treatment, Adverse Effects, Economics,
Community and Institutional Issues, Case Studies, and Conclusions and
Summary.
If you could only read one chapter in this helpful book for policy
makers and practitioner, I recommend Conclusions and Summary by
Valentina Lazarova covers assessment of the feasibility of using
recycled water for irrigation, good agronomic practices for irrigation
with recycled water, negative impacts of irrigation water on plants and
corrective actions, management practices and corrective actions for
improvement of the operation of water-reuse treatment schemes,
successful participation programmes improved public acceptance, and
successful initiatives to address legal and institutional issues. The
flow charts and tables are very useful, especially Table 13.1 "Main
Elements to be Considered for Planning of Water Reuse for Irrigation
and Factors Influencing Decision" for agricultural irrigation, and
landscape and turfgrass irrigation with columns for crop type, soil
properties and hydrogeology, irrigation, method, water quality, and
miscellaneous. Table 13.2 "Summary of Successful Practices of
Irrigation with Recycled Water (Agricultural Crops, Turfgrass, and
Landscape Ornamentals," Table 13..3 "Guidelines for Identification
of Some Common Negative Impacts of Irrigation Water on Plants and
Recommended Corrective Actions," Table 13.4 "Examples of Good
Operational Practices and Corrective Actions to Improve the Reliability
of Wastewater Treatment, Storage, and Distribution," and Table 13.5
"Main Institutional Issues to be Addressed for Successful Development
of Water-Reuse Projects for Irrigation."
Several chapters were especially interesting to me are discussed here,
in addition to the last chapter on Conclusions and Summary notes just
above. The Challenges and Sustainability by Valentina Lazarova and
Akiça Bahri lists 26 "countries leading in water reuse activity and
countries still using raw sewage for irrigation." Those leading in
reuse are (Chile, Sweden), medium reuse (Argentina, Belgium, Canada,
France, Italy, Namibia, Tunisia, United Kingdom), high reuse
(Australia, Japan, Jordan, Oman, Spain, and Arizona and Florida), and
intensive reuse (Israel, Kuwait, Saudi Arabia, United Arab Emirates,
California). Those still using raw sewage are China, Egypt, India,
Mexico, and Morocco. The most proactive U.S. states are listed as
Arizona, California, Florida, Hawaii, Nevada and Texas for agricultural
and landscape irrigation, groundwater recharge, industrial uses, urban
uses, and other uses.
Water Quality Considerations by the wise Valentina Lazarova, Herman
Bouwer, and Akiça Bahri wisely address parameters with health and
agronomic significance, and sampling and monitoring strategies, noting
wisely that "water quality is the most important issue in water reuse
systems that determines the applicability and safety of the use of
recycled water for a given reuse application." Wastewater effluent
from treatment facilities could be enormously improved were more use
were made of desalination systems for salt reduction and oxygenation
systems rather than standard aeration systems for organic matter
reduction in the wastewater treatment train, but this is quite
expensive and currently largely impractical.
Herman Bouwer's insightful Adverse Effects of Sewage Irrigation on
Plants, Crops, Soil, and Groundwater addresses healthy environment and
sustainability, compounds with potential adverse effects on recycled
water for irrigation, behavior of some compounds (salt, nutrients,
disinfection by-products,, pharmaceuticals and other organics) during
irrigation with sewage effluent, salt and groundwater water-table
management (salt loadings, salt tolerance of plants, salty water
management, salinity management in south-central Arizona (U.S.)). I
suggest that there would be enhancement in salt water management with
the use of halophytes or salt-water loving plants where climatic
conditions are favorable, like ornamental and landscaping Batis, Cresa,
and Susubia, and landscaping and potentially economic Atriplex,
Salicornia, and mangroves, which may add economic benefits as well from
firewood, charcoal, paper products, honey, oil seed, fodder, perfumes
and other goods, and created wetlands and habitats, and even
large-scale carbon sequestering to combat climate change, bird
sanctuaries, and eco-tourism opportunities.
Valentina Lazarova's very helpful Wastewater Treatment for Water
Recycling is the longest chapter at 110 pages. It contains basic
design and operational information and, though suggested "should be
used only as illustration and guidelines for the choice and preliminary
design of water reuse treatment trains," it is comprehensive and
insightful. The inclusion of biofilm reactors which originated in the
food-waste processing industry, as well as non-conventional natural
systems where much land is available (lagoons, wetlands,
infiltration-percolation, soil-aquifer treatment) are refreshing,
though my experience indicate that the natural systems are most effect
as polishing treated effluent rather than treatment per se. Inclusion
of advanced tertiary treatment and disinfection (including membrane
filtration and membrane bioreactors), storage and distribution of
recycled water, criteria for selection of appropriate polishing process
before irrigation are especially interesting and insightful.
Economics of Water Recycling for Irrigation by Joe Morris, Valentina
Lazarova, and Sean Tyrrel covers general principles, financial and
economic analysis, benefits and influencing factors, recycling
components, water supply and recycling options for irrigation, criteria
for setting prices for recycled water, pricing instruments, examples
and conclusion. The "critical determinants are... the quality of the
source and receiving waters and the quality of required for
irrigation" for recycling options. Costs of options includes both
initial capital costs and annual operating costs, and pricing
instruments include flat monthly charges as $/ha/month, flat charges
per unit volume ($/cubic meter), base fee plus volume charge,
winter/summer adjusted rate, ascending rate, declining block rate, time
of day-based rate (peak/off peak), time or pay-based contracts, and
customer-specific negotiated rate. Examples of recycled water sale
prices in California provided for Long Beach, Marin County, Milpitas,
Orange County, San Jose, Irvine Ranch, North Coty (San Diego),
Carlsbad, East Bay Municipal (Oakland), Otay, and West Basin Municipal
(Carson, Los Angeles County), as percentage of potable water rates.
These rates ranged from 53 to 100 percent and included irrigation,
landscape, indirect potable reuse, industrial use, and urban uses and
irrigation, aquifer recharge and industrial uses in West Basin
Municipal at 80 percent (53 to 90 percent). I would have preferred
attention to applied economics to life cycle analysis of wastewater for
recycling even in the format that several states including California
require for state approvals for bonding purposed.
In my experience, agricultural water is rarely priced appropriately,
even in developed countries, and if so even rarely enforced developing
countries where it is priced, especially in arid lands where fresh
water is scarce, and it is unlikely that farmers in these areas would
pay even the operation and maintenance (O&M) costs for wastewater
treatment for recycled water for irrigation. Nonetheless, there are
cost-benefit models which assume cash flows and benefits to recycled,
usually not applied to developing countries where median domestic
national incomes (MDNI) are in the several $100s/year as opposed to
developed countries where MDNIs are in the several $10,000s/year.
Some countries, like Egypt, which have federal programs to provide
water to farmers for irrigation, do not directly charge farmers for
irrigation water may charge an annual land-use property tax on
agricultural land which is irrigated and non-irrigated. The irrigated
land rate is fixed and not related to irrigation water use, cropping
pattern, or irrigation system; the farmers, of course, must pay the
cost of uplifting branch canal water to on-farm canals. Therefore,
farmers on same-sized irrigation plots would pay a flat land-use
property tax, whether they were drawing water for relatively high
water-use crops like sugarcane, rice, bananas, and alfalfa, or
relatively low-water use crops like cereals, cotton, corn, and maize.
In addition, though some countries, like Egypt, issue annual crop
permits and have public outreach programs to encourage farmer
conformance to federal crop production policies, government surveys
typically find that actual cropping exceeds permitted cropping by
several fold for high-priced crops like sugarcane and rice. Egypt, of
course is arguably the home of irrigation farming, and invented the
Nilometer which was a series of steps into the Nile at several
locations to asses the availability of water for irrigation and other
uses, and was used in ancient Egypt as a sort of Consumer Price Index
or Federal Reserve Rate to set the tax rate for the country; in years
when the Nile was low, taxes declined because low Nile would depress
the agricultural economy; when the Nile was high, it was the reverse.
In addition, the major capital and O&M costs for supplying water to
farmers in through national canals in developing is borne by the
federal government (or by the federal and state entities in India as
India is more of a continent and its states are fairly independent as
countries) often with donor support. This practice unfortunately
encourages and perpetuates this non-user supported practice which would
be culturally and politically difficult to modify. The pricing
mechanism itself does not encourage, for example, greenhouse irrigation
or water conservation, though there is extensive greenhouse agriculture
in the Jordan Valley in Jordan, and throughout much of Israel which has
been very innovative in irrigation farming, even developing and
implementing saline water irrigation systems in the Negev and
elsewhere.
Case Studies of Irrigation with Recycled Water gives examples from El
Mezquital (Mexico) by Blanca Jimenez, Costa Brava (Spain) by Lluís
Sala and Xavier Millet, and Monterey County (U.S) by Bahman Sheikh. El
Mezquital emphasizes "the choice of appropriate treatment to improve
the health safety of agricultural irrigation with wastewater" as
Mexico more commonly uses raw wastewater which leads to significant
health problems. Costa Brava emphasizes golf irrigation with recycled
water. Monterey emphasizes challenges of irrigation of food crops with
recycled water where good management practices and communication
strategy among stakeholders are essential even where there is a high
level of treatment and extensive water-quality monitoring. On a
political note, I observed the use of political quid pro quo over
recycled water use. Some Arabian Gulf States do not import crops from
countries which supported and even rejoiced in Saddam Hussein's 1990
Iraqi invasion of Kuwait which took over Kuwait, threatening the
regional oil fields, and sent Iraqi missiles into non-provocative
Israel and Saudi Arabia, and Saddam's responses to the U.S.-lead Gulf
War I or Operation Desert Storm in 1991. Operation Desert Storm
removed Iraqi forces from Kuwait with support of Afghanistan,
Australia, Bahrain, Bangladesh, Belgium, Britain, Canada,
Czechoslovakia, Egypt, France, Germany, Honduras, Hungary, Italy,
Kuwait, New Zealand, Niger, Oman, Poland, Qatar, Romania, Saudi Arabia,
South Korea, Syria, and United Arab Emirates per www.desert-storm.com.
The Gulf States which do not import crops from these Saddam-supported
countries described above say that they do not import crops grown with
recycled water because of health issues, and indeed there are serious
health issues associated with improperly treated wastewater, though
some Gulf states use recycled water themselves in their own crop
production but of course they have more control on irrigation water
quality.
Barney
Barney P. Popkin, Water Resources & Environmental Management Consultant
Barney
Irrigation
Barney P. Popkin, Water Resources & Environmental Management
bppo...@yahoo.com
February 26, 2005
CRC Press's 2005 Water Reuse for Irrigation: Agriculture, Landscapes,
and Turf Grass, edited by the talented and insightful Valentina
Lazarova and Akiça Bahri (1) provides, among other things, some
insight to the Increase in Crop Productivity by Use of Wastewater for
Agricultural Irrigation. Table 1.3 in the chapter on Challenges and
Sustainability by Valentina Lazarova and Akiça Bahri lists 26
"countries leading in water reuse activity and countries still using
raw sewage for irrigation." Those leading in reuse are low reuse
(Chile, Sweden), medium reuse (Argentina, Belgium, Canada, France,
Italy, Namibia, Tunisia, United Kingdom), high reuse (Australia, Japan,
Jordan, Oman, Spain, Arizona and Florida), and intensive reuse (Israel,
Kuwait, Saudi Arabia, United Arab Emirates, California). Those still
using raw sewage are China, Egypt, India, Mexico, and Morocco. The
most proactive U.S. states are listed as Arizona, California, Florida,
Hawaii, Nevada and Texas for agricultural and landscape irrigation,
groundwater recharge, industrial uses, urban uses, and other uses.
Consultant Bahman Sheikh presents a case study to demonstrate the
feasibility of irrigation of food crops, including vegetables eaten
raw, with recycled water in the northern part of the Salinas Valley,
Monterey County, California (Chapter 12.3, Monterey County Water
Recycling Projects: A Case Study in Irrigation Water Supply for Food
Crop Production (2)), noting "it is estimated that 70 percent of all
artichokes produced in the U.S. are irrigated with recycled water."
In addition to artichokes, other food crops irrigated in the valley
with recycled water include strawberries, iceberg lettuce, broccoli,
fennel, celery, cauliflower. The case study notes "It is now amply
demonstrated, both in pilot and full-scale operations, that this use of
recycled water is safe, that it does not impact the soil negatively,
and that it does not drive consumers away from purchasing produce
irrigated with recycled water. As a matter of fact, farmers are
experiencing increased yields on fields irrigated with recycled water
over those receiving well water alone." Of course, we are talking
here of "tertiary recycled water is the only source of irrigation
that is thoroughly disinfected, is virtually free from pathogens, and
has consistent, known chemical and microbiological characteristics."
The chapter concludes with "The safety, long-term benefits, and
public acceptance of crops grown with recycled water have now been
established in several major locations in California, including Irvine
(Orange County), Santa Rosa (Sonoma County), and Napa and Monterey
County. The long-term direction for recycled water in California
appears to be toward more high-value uses of water, consistent with the
increased demand, uncertain supplies, and a greater public perception
of the scarcity of water resources." See (3, 4).
However, developing countries may not be as careful in meeting
California Code of Regulations Title 22 strict regulations or
equivalents to assure that recycled water is safe and acceptable for
the use in irrigation of food crops. For example, Blanca
Jimenez-Cisneros with the National Autonomous University of Mexico
presents another case study as Chapter 12.1 (El Mezquital, Mexico: The
Largest Irrigation District Using Wastewater (5). She notes that
"with the use of untreated wastewater, agricultural productivity has
been increase up to 150 percent for some crops (See Table 1 below).
Nevertheless, serious health problems have been observed:
gastrointestinal diseases caused by helminthes (eggs) occur 16 times
more often in children 5 to 14 years of aged that in the equivalent
zones using fresh water (6). Similar health problems associated with
poor microbiological quality of reclaimed untreated wastewater have
been reported in other developing countries (7). The major reason is
the low wastewater-treatment level; the percentage of treated
wastewater varies from 0 to 30 percent in some countries in Latin
America, Africa, and Asia (8)."
Table 1 below shows increases in productivity by use of water for
agricultural irrigation in the Mezquital Valley for corn, barley,
tomato, forage oats, alfalfa, chile, and wheat. However, Table 2 shows
a comparison of morbidity in Mezquital Valley and a similar zone that
uses clean water for irrigation, the rates presumably related to
irrigation water and crop quality. Finally, Table 3 shows the
microbial content in wastewater for different countries for Helminth
eggs, Salmonella, and Protozoan cysts. According to Jimenez-Cisneros
(5), "due to the particular situation in Mexico, the local standard
that controls water quality for irrigation was modified in 1996 to
consider a value of <1 helminth egg/L and <1000 fecal coliforms
(FC)/100 mL for all type of crops (10) and 100 FC/100 mL for crops that
are consumed cooked. The value of 5 eggs/L was established on the
basis of the basis of the feasible value that conventional biological
or physiochemical processes could achieve without filtration (11, 12).
Organic matter and suspended solids are not limited in this regulation,
since the former is mandatory in soils, where suspended solids must be
removed to meet the required helminth egg concentration."
Table 1. Increase in Productivity by Use of Wastewater for Agricultural
Irrigation in the Mezquital Valley (4, 9)
Productivity (ton/hectare)
Crop Wastewater Fresh water Increase (percent)
Corn 5.0 2.0 150
Barley 4.0 2.0 100
Tomato 35.0 18.0 94
Forage oats 22.0 12.0 83
Alfalfa 120.0 70.0 71
Chile 12.0 7.0 70
Wheat 3.0 1.8 67
Table 2. Comparison of Morbidity in Mezquital Valley and a Similar Zone
that Uses Clean Water for Irrigation (4, 6)
Microorganism Affected Rate of morbidity
population
by age Wastewater- Fresh-water
irrigated irrigated A/B ratio
zone (A) zone (B)
Ascaris humbricoides
0-4 15.3 2.7 5.7
5-14 16.1 1.0 16.0
>15 5.3 0.5 11.0
Giardia lamblia
0-4 13.6 13.5 1.0
5-14 9.6 9.2 1.0
>15 2.3 2.5 1.0
Entamoeba histolytica
0-4 7.0 7.3 1.0
5-14 16.4 12.0 1.3
>15 16.0 13.8 1.2
Table 3. Microbial Content in Wastewater from Different Countries (4,
7)
Parameter Concentration Country
Helminth eggs, eggs/L 6-98 Mexico
1-8 U.S.A.
166-202 Brazil
up to 60 Ukraine
up to 9 France
up to 840 Morocco
Salmonella spp., MPN/100 mL 1,000,000-1,000,000,000 Mexico
1,000-1,000,000 U.S.A.
Protozoan cysts, cysts/L 978-1814 Mexico
28.4 U.S.A.
So serious is helminthiases as common diseases in the developing world
that an average of 27 percent of the population (650 million people) is
estimated to be infected, with up to 90 percent in poor areas (5, 13,
14). In developed countries, helminthiases reach up to 1.5 percent of
the population (5, 15). According to Jimenez-Cisneros (5), "these
diseases are endemic in Africa, Central America, South America, and the
Far East, where poverty and unsatisfactory conditions are common. They
are transmitted through helminth egg ingestion form vegetables
irrigated with polluted water. Helminth eggs are resistant to
chlorine, ultraviolet light, and ozone. Infective doses are very low
(1-10 eggs/L) compared to those for bacteria. Ascaris is the most
common helminth found in wastewater and sludge, and it is also the most
resistant to wastewater treatment and medications. The physical
properties of helminth egg (20-80 micrometers, specific density
1.036-1.238) greatly influence their removal from wastewater (16). As
part of suspended solids, helminth eggs are removed by means of
treatment processes such as settlers, lagoons,
coagulation-flocculation, and filtration."
Citations:
(1) Lazarova, Valentina and Bahri, Akiça, eds., 2005. Water Reuse for
Irrigation: Agriculture, Landscapes, and Turf Grass. CRC Press, Baton
Rouge.
(2) Sheikh, Bahman, 2005, Monterey County Water Recycling Projects: A
Case Study in Irrigation Water Supply for Food Crop Production.
Chapter 12.3, in Lazarova, Valentina and Bahri, Akiça, eds., 2005,
Water Reuse for Irrigation: Agriculture, Landscapes, and Turf Grass.
CRC Press, Baton Rouge.
(3) Sheikh, Bahman, et al, 1998, Tertiary Reclaimed Water for
Irrigation of Raw-Eaten Vegetables. Chapter 17, in Asano, Takashi,
ed., 1998, Wastewater Reclamation and Reuse, CRC Press, Baton Rouge.
(4) Bruvold, W.H., 1972. Public Attitudes Toward Reuse of Reclaimed
Water. Contribution, University of California Water Resources Center,
173.
(5) Jimenez-Cisneros, Blanca, 2005, El Mezquital, Mexico: The Largest
Irrigation District Using Wastewater. Chapter 12.1, in Lazarova,
Valentina and Bahri, Akiça, eds., 2005, Water Reuse for Irrigation:
Agriculture, Landscapes, and Turf Grass. CRC Press, Baton Rouge.
(6) Cifuentes, E., Blumental, U., Ruiz-Palacios, G., and Bennett, S.,
1991/1992, Health Impact Evaluation of Wastewater in Mexico, Public
Health Review, Vol. 19, No. 243.
(7) Jimenez-Cisneros, Blanca, 2003, Health risks in aquifer recharge
with recycle, in Chapter 3, State of the Art Report on Health Risks in
Aquifer Recharge Using Reclaimed Wastewater, Aertgeerts, R. and
Angelakis, A, eds, World Health Organization Geneva.
(8) WHO/UNICEF, 2000, Global water supply and sanitation assessment
report, Joint Monitoring Program for Water Supply and Sanitation,
Geneva.
(9) Jimenez-Cisneros, Blanca and Chavez, A., 1998, Removal helminth
eggs in an advanced primary treatment with a sludge blanket,
Environmental Technology, Vol. 19, No. 1061.
(10) WHO, Health Guidelines for the Use of Wastewater in Agriculture
and Aquaculture, Report of a WHO Scientific Group, Technical Report
Series 778, World Health Organization, Geneva, 1989
(11) Jimenez-Cisneros, Blanca and Chavez-Mejia, A., 1997, Treatment of
Mexico City wastewater for irrigation purposes, Environmental
Technology, Vol. 18, No. 721.
(12) Landa, A., Capella, A., and Jimenez, B, 1997, Particle size
distribution in an effluent from an advanced primary treatment and its
removal during filtration. Water Science Technology, Vol. 36, No. 4,
p. 159.
(13) Bratton, R. and R. Nesse, 1993, Ascariasis: an infection to watch
for in immigrants. Postgraduate Medicine, Vol. 93, no. 171.
(14) Wani, N. and R. Chrungo, 1992, Biliary ascarisis: surginal
aspects. World Journal of Surgery, Vol. 16, No. 976.
(15) World Health Organization, 1997, Amoebiasis, an expert
consultation. Weekly Epidemiological Record, Vol. 14, Geneva.
(16) Ayres, R., 1989, Enumeration of parasitic helminthes in raw and
treated wastewater A contribution to the international drinking to
water supply and sanitation decade 1981-1990, Leeds University,
Department of Civil Engineering.