the reuse of wetland-treated oilfield produced water ...

THE REUSE OF WETLAND-TREATED OILFIELD PRODUCED WATER FOR SALINE IRRIGATION Authors:

¹Stephane Prigent, ¹Asma Al-Hadrami, ²Tom Headley, ³Wail Harrasi, ¹Alexandros I. Stefanakis

Presenter:

Stephane Prigent, PhD ¹Bauer Nimr LLC, P.O. Box :1186, Postal Code 114, Al Mina, Muscat, Sultanate of Oman, [email protected] ²The Water and Carbon Group, P.O. Box 294, Brisbane, QLD, Australia ³Petroleum Development Oman

Abstract Wastewater is increasingly viewed as an additional source that can provide a new source of good quality water. Among the various industrial wastewater types, produced water from oilfields is one of the most challenging due to the presence of toxic and inorganic pollutants, while most of this water occurs in remote and/or desert environments. Bauer Nimr has constructed and currently operates one of the largest constructed wetland plants in the world in the desert of Oman. This plant receives and treats more than 115,000 m³/d of produced water from a nearby oilfield. The treated effluent, although is oil-free (less than 0.5 mg/L hydrocarbons content), has a high salinity, which is usually prohibiting for potential reuse. Bauer Nimr, in partnership with Petroleum Development Oman, designed, constructed and is operating a large-scale experimental project to assess the reuse possibilities of oilfield-produced water for irrigation of salt tolerant plants, following treatment in the constructed wetland system. The experimental agricultural field of 22 ha is adjacent to the wetland treatment facility. In this project, 13 different salt tolerant plant species (e.g., acacia nilotica, conocarpus lancifolius, cotton, ricinus communis, salicornia bigelovii etc.) will be irrigated with three different water qualities abstracted from three different points along the wetland length (1/3, 2/3 of length and final effluent) under different irrigation methods (flood irrigation, drip irrigation, bubblers and sprinklers). The overall project goal is to evaluate the effects of produced water quality and irrigation method on the growth rate and yield of different halophytic plants under desert field conditions. This paper presents the general setup of the experimental agricultural water reuse field, the main goals and the first results obtained during the first months of operation.

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I.

INTRODUCTION

Water scarcity is a major issue in many countries around the world. Wastewater, either municipal or industrial, is increasingly viewed as an additional source that can be added to the water balance and provide a new source of good quality water. Industrial wastewater reuse represents high technical challenges, considering the varying nature of the different pollutants found in industrial effluents. Among the various types, produced water from oil fields is probably the most challenging due to the toxic and inorganic pollutants present in this water and the fact that most of this water sources occur in remote and/or desert environments. The water produced during the extraction of oil and gas represents one of the largest industrial waste streams throughout the world [1]. Produced water may include water from the reservoir, natural formation water and water injected into the formation, along with any chemical substances used during the production and treatment processes. Generally, it is considered as the water volume that is returned to the surface through an extraction well borehole. The global produced water treatment market size is continuously growing and estimated to exceed $8.0 billion by 2019 [1]. Stricter environmental policies and energy sector growth drive this environmental vision. The North American region is the largest market for produced water treatment; more than 20 billion barrels of produced water are annually produced in the USA [2]. Middle East market also remains a key growth area due to increasing awareness and fresh water shortage.

1.1

Technologies for produced water treatment

In the oil and gas industry, produced water management represents a major challenge given that there should be a balance between extraction profits and public health and environmental protection. Gradually, the perception of produced water shifted and it is increasingly viewed as a useful by-product, while the environmental impact of produced water led to more stringent standards for discharge [3]. Produced water usually contains high levels of salinity, which is energy-intensive to treat. Desalination of produced water is a method widely applied to improve produced water quality and make it appropriate for demanding reuse options [4]. There is a series of method applied for produced water treatment and desalination, mostly mechanical, such as membrane filtration technology [5-7], thermal technologies [3,8,9], aerated filters [3,10], flotation [3,11,12] and electrodialysis [3,8,13], among others. However, the main disadvantage of these methods are their high operational and maintenance costs due to high energy consumption and frequent mechanical failure.

1.1.1

Wetland Technology

Over the last two decades, the alternative green technology of Constructed Wetlands (CWs) has attracted more attention as a natural process for produced water treatment. CWs have been proved effective in the treatment of domestic and municipal wastewaters [14-16]. The high treatment capacity of the system enabled the use of this technology for the treatment of various industrial wastewaters as well [17]. Petrochemical industry is one of the fields where wetland technology is rapidly developing. CWs can provide an effective, cost-efficient and ecological solution to the problem of produced water treatment. Wetland systems are particularly appropriate for production fields in remote areas, where available land is also adequate. Currently there are many wetland systems in various facilities such as refineries, oil and gas fields and pumping stations [18]. One of the largest wetland systems worldwide The International Desalination Association Conference on Water Reuse and Recycling – Nice, France

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treating produced water from an oilfield exists in Oman [19,20]. Other systems exist in the USA [21], in Sudan [22], in China [23]. The potential of the system to effectively treat produced water enabled at the same time research efforts to further improve the efficiency and gain fundamental knowledge on the processes and parameters that regulate and/or affect the performance [24,26]. Plant species represent a basic element in the wetland setup and play a certain role in the treatment process. However, the effects of produced water on plants are not yet clear; for example, it is not well understood the impact on the growth characteristics of different wetland plant species.

1.2

Reuse of produced water

The tendency and practice today dictates a more efficient use of water resources, both in urban and rural environments. A major mechanism for greater efficiency is the reuse of water that would have been normally discarded into the environment after use. Water reuse for agricultural irrigation is often viewed as a positive means towards water recycling due to the potential large volumes of water that can be exploited in this way. Recycled water can have the advantage of being a constant and reliable water source, while it reduces the amount of fresh water extracted from the environment [27,28]. The major concern, however, has to do with the potential impact of the quality of the recycled water, both on the irrigated crop as well as on the end users of the crops [28]. Water reuse applications are usually viewed an environmental friendly practice serving the sustainable water management approach and as an economically beneficial practice [29, 30]. Produced water reuse is a challenging task due to the variety of pollutants present in this water, e.g., high levels of salinity (i.e., total dissolved solids – TDS), oil and grease, dispersed oil, heavy metals, dissolved organic compounds and chemical that may have been used in the production. Thus, high-level treatment is usually applied to achieve deoiling, degassing, desalination, organic compounds removal, suspended solids removal and heavy metals removal, in order to deliver a water quality that could potentially reused. However, the achievement of all these treatment goals requires the combination of different treatment technologies and the use of physical, chemical and biological treatment processes, which is translated in high treatment costs and limited cost-efficiency. Therefore, the implementation of wetland technology for produced water treatment is increasingly viewed as a sustainable alternative to significantly improve the quality of the treated effluent. It is understood that irrigation with treated produced water could be an attractive and sustainable option for produced water management. This option could represent an innovative approach, especially if it is applied in regions with limited water resources, that would offer added-value to this water source if it is combined with the production of beneficial products such as biofuel and biomass material. However, there are many questions still to be answered regarding the selection of appropriate plant species that could be irrigated with treated produced water and the ability of these plants to grow and provide addedvalue products. Additionally, such efforts should also be estimated from the financial point of view, to determine whether they could represent am economically viable solution. 1.2

Scope of project

Based on the above, the aim of this experimental project (further called as Biosaline Agriculture Research Project – BARP) is to investigate the establishment and growth of 13 different plant species The International Desalination Association Conference on Water Reuse and Recycling – Nice, France


irrigated with oilfield produced water treated in a constructed wetland system under desert field conditions. Specific objectives of the project are the investigation of impact of (i) different water qualities, i.e., water abstracted from three different points along the constructed wetland length, (ii) different irrigation methods, i.e., flood irrigation, drip irrigation, bubblers and sprinklers and (iii) to evaluate the effects of different water qualities and irrigation methods on the growth characteristics and yield of the selected plant species.

II.

MATERIALS AND METHODS

2.1

Description of Constructed Wetland plant for produced water treatment

The treatment facility is located in the desert of the southeastern Arabian Peninsula, in Nimr, approximately 700 km south of Muscat the capital of Oman.

Constructed Wetland

Desert

N

Figure 1: Location of the Constructed Wetland treatment plant in the desert of the south eastern Arabian peninsula in Oman (left) and aerial picture of the Constructed Wetland system and the surrounding desert (right). The Nimr Water Treatment Plant (NWTP) has the capacity of treating 115,000 m³/day of produced water using 350 ha of Surface Flow Constructed Wetland (SFCW) and 500 ha of evaporation ponds. Produced water is sent through a pipeline to the Turn-Over-Point (TOP) of the plant, where separation and recovery of the majority of oil from the produced water takes place, using a series of hydro-cyclone oil separators. Then, the produced water is distributed in the SFCW via a long buffer pond. The 350 ha of SFCWs are divided into 9 parallel tracks, each consisting of four 10 ha wetland terraces in series, operating with gravity flow (Figure 2). Samples of native wetland plant species were collected throughout Oman (Wadis, Coastal lagoons), propagated in the onsite nursery and then planted in the SFCW. Approximately 3 million plant seedlings have been planted to date. Most of the treated water flows into a series of EPs which are used for disposing of the majority of the production water through evaporation resulting in salt formation. The facility was commissioned in November 2010 and will operate for at least 20 years. The size of this system makes it is one of the world’s largest constructed wetlands. It should be noted that the SFCW is now well integrated and accepted by the wildlife and provide a comfortable stop-over for more than 120 migratory bird species between Asia and Africa. The International Desalination Association Conference on Water Reuse and Recycling – Nice, France


Buffer pond

Produced Water entering the SFCW

Water Quality 1 Extraction Point

Constructed wetland

Water Quality 2 Extraction Point Water Quality 3 Extraction Point

Evaporation Ponds

Biosaline Agriculture Research Area

Salt works

Gate House, Entrance of the NWTP

Figure 2. General overview of the SFCW facility showing each stage in the system, the location of the experimental irrigation project area and the water quality extraction points. The air temperature can reach up to 50˚C during the summer months. The composition of the produced water from the nearby Nimr Oilfield is brackish with influent Total Dissolved Solids (TDS) concentration ranging between 7,000 and 8,000 mg/L and increasing along the wetland terraces due to evapotranspiration losses. Furthermore, the produced water is characterized with a low nutrient concentration, i.e., total nitrogen and total phosphorus concentrations lower than 1 mg/L.

2.2

Description of the experimental setup

The BARP field is located on the left side of the access road after passing the entrance of the NWTP through the gatehouse (Figure 2). Two main irrigation areas of 11 ha each, named flood irrigation and overhead irrigation, respectively, have been constructed in this area. Each irrigation area consists of three blocks of about 3.7 ha each, receiving three different water qualities with the use of a pumping system. Each of the blocks is divided into two sub-blocks made of six irrigations zones. In each sub block, two irrigation zones are planted with perennial plant species and one zone with annual plant species and grasses. 2.2.1

Water quality

The International Desalination Association Conference on Water Reuse and Recycling – Nice, France


Based on the water quality data collected at the system since its commissioning period, the oil content decreases rapidly as water moves through the wetland terraces and is less than 1 mg/L after the 2 nd terrace. Therefore, the water after this terrace is considered suitable for irrigation. The oil in water (OiW) is further decreased after the 3rd terrace, reaching levels below the detection limit (< 0.5 mg/L). However, other parameters such as Boron and salinity increase along the length of the SFCW and may have a potential impact on plant growth. Thus, it was decided to apply three different water qualities, pumping produced water from respective points along the wetland length (Figure 2) with minimum hydrocarbon concentration: 2.2.2

Outlet point 1.2 = Water Quality 1 (WQ1), Outlet point 1.3 = Water Quality 2 (WQ2), Outlet point 1.4 = Water Quality 3 (WQ3). Selected plant species

Perennial and annual plant species have been selected according to the climate and water characteristics, as well as the potential commercial value of the end products. Based on the below listed criteria, the selected plant species are presented in Table 1. -

Tolerance to brackish water (up to 12,000 ppm TDS), Compatible with the hot and dry desert climate, Tolerance to water logging due to flood irrigation, Plants with valuable commercial end-product such as biofuel, timber or carbon credits, Non-invasive and with limited risk for the local biodiversity. Table 1: Perennial, annual plant species and grasses investigated in the BARP. Plant species

Common name

End product

Growth form

Acacia nilotica Acacia ampliceps Casurina equisetifolia Conocarpus lancifolius

Acacia (Qarat) Acacia Casurina Kuwaiti tree

Wood / honey wax Wood / honey wax Wood / windbreak Wood / windbreak

Perennial tree Perennial tree Perennial tree Perennial tree

Eucalyptus camaldulensis Prosopis cineraria

Red river gum Ghaf

Wood / windbreak Wood

Perennial tree Perennial tree

Distichlis spicata Paspalum vaginatum

Distichlis grass Salt grass

Forage - landscaping Forage – landscaping

Grass Grass

Cotton spp. Brassica napus Cyamopsis tetragonoloba Ricinus communis

Cotton Canola Guar Castor

Textile Oil - Biofuel Guar gum Oil – Biofuel

Annual Annual Annual Annual

Salicornia bigelovii

Dwarf Saltwort

Oil - Biofuel

Annual



2.2.3

Irrigation methods

Two general methods of irrigation are used: flood and overhead. Sprinkler, drip and bubbler systems are three different techniques used for the overhead irrigation. Table 2 summarizes the irrigation methods used for the selected plant and grass species. Table 2: Irrigation methods of the BARP applied to each plant species. Overhead irrigation

Plant Species

Flood irrigation

Sprinkler

Drip

Bubbler

Acacia nilotica

X

-

-

X

Acacia ampliceps Casurina equisetifolialia Conocarpus lancifolius

X X X

-

-

X X X

Eucalyptus camaldulensis Prosopis cineraria

X X

-

-

X X


X X

X X

-

-

Cotton spp

X

-

-

X

Brassica napus Cyamopsis tetragonoloba Ricinus communis Salicornia bigelovii

X X X X

-

X -

X X X

Flood irrigation: in total, there are six similar irrigation sub-blocks constructed in the flood irrigation area. Treated produced water feeding is achieved by creating parallel wet furrows of 55 m length along the field length towards the flow direction. Water is applied to the top end of each wet furrow and flows down the channel by gravity. Each plant is planted on the ridge between furrows to ensure that the root system is not saturated with water. Wet furrows geometry varies between perennial, annual plants and grasses. In total, there are 36 ridges for each irrigation zone for the perennial plants and 16 for the annual plants. In general, salt accumulation is managed with flood irrigation by periodically flushing and leaching the salts from the upper soil profile for annual plants and grasses. For the long-term growth of the perennial plant species, the effect of salt accumulation is decreased using alternate wet and dry furrow irrigation. This is accomplished by irrigating every other furrow and leaving alternating furrows dry (Figure 3A). In this way, salts are pushed across the bed from the irrigated side of the furrow to the dry side. Annual plant species are planted on both sides of the ridges above the water level (Figure 3B). There is no management practice on the accumulation of salt for those plants as the soil is to be replaced annually. A mixture of compost and local soil is mixed before planting at the start of each growing season. Selected grasses are flooded in nine furrows each of 3 m width (Figure 3C).



Figure 3. Cross section of the flood irrigation field (A = perennial plants; B = annual plants; C = grasses). Overhead irrigation: produced water is distributed using an extensive hydraulic PVC pipe network that conveys water from the different PW extraction locations to the blocks. The water is applied through the bubbler emitters placed in the basins surrounding each perennial plant and through the sprinklers and drip lines for the annual plant species and grasses. The water is then directly infiltrated into the soil and wets the root zone. 1) Bubbler irrigation: The main supply line from each water quality extraction location is connected to an HDPE manifold pipe (Figure 4). To ease installation and maintenance of the irrigation system, a series of 20 HDPE lateral lines are installed at the ground level on each side of the manifold every 5 m along the length of the 55 m long field. Feeder lines provided with bubblers are installed on the top of the soil pile and each of the bubbler is operating with a nominal flow rate of 8.7 L/min. A pile of soil of approximately 1 m height and 2.5 m diameter at the base enables the vertical drainage of salts from the root zone and gives enough capacity for root growth. Control of salt accumulation is achieved with bubblers, by irrigating at a higher rate than what is actually required by the plants. This surplus of irrigation water pushes salts deeper into the soil profile, so that salts do not accumulate around the plants root system. Figure 6 shows a section of the soil pile for perennial plant species growth. 2) Sprinkler irrigation: Sprinkler irrigation zone is 55 m long and 44 m wide. A network of 180 mm lateral PVC pipes follows the boundaries of the sprinkler irrigation zone. A total of 7 vertical sprinkler made of 20 mm PVC pipes are installed along the length of the field and evenly spaced every 6 m. The sprinkler raiser is installed 1 m above the ground surface. Each sprinkler irrigation zone has a total of 14 sprinkler raisers made from copper to prevent rust. Sprinkler irrigation method has been selected for grass species. A picture of the sprinkler irrigation field is presented in Figure 5. The International Desalination Association Conference on Water Reuse and Recycling – Nice, France


Figure 4. Cross-section of a perennial tree pile under bubbler irrigation method.

Figure 5. Sprinkler irrigation zone at the beginning of the experiment. 3) Drip irrigation: Drip irrigation zone is 55 meters in length and 31 meters width. The drip irrigation zone consists of three drip irrigation fields provided with 20 flexible above ground drip lines each of 16 mm external diameter. Emitters are placed every 0.5 m along the drip line and enable to discharge a flowrate of 55 mL/min. High pressure through the drip irrigation lines reduces the chances of salt accumulation within the emitters. Figure 6 shows drip irrigation in the BARP.



Figure 6. Drip line Irrigation zone at the beginning of the experiment.

2.3

Soil preparation

The project irrigation area is mostly covered with a bed rock, thus it was decided to backfill the flood irrigation area with approximately 65 cm thickness of local soil from stockpiled construction material left over from the NWTP construction phase. The soil addition was necessary to provide substrate for plant root development. A 35 cm top soil layer of screened red soil (0-20 mm) was added above the construction material to enable the planting of the different plant species. Ridges were then created by cutting furrows with construction equipment. Mushroom compost was placed at each marked plant station for the perennial trees at a rate of 1.5 kg per plant station. The same rate was also applied to the annual plant stations on the top of each soil pile. After the application, the compost was mixed with the soil at each plant station. Mushroom compost was applied before planting in order to improve the soil structure and the water holding capacity of the soil and to release nutrients to the plants for optimum plant growth. 2.4

Planting

Different methods of planting were implemented according to the agronomic recommendations for each type of plant species. Planting methods used were (a) seed sowing and (b) transplanting. Propagation of plant species took place either in Muscat nursery or in the onsite nursery. Table 3 summarizes the planting methods, planted populations and propagation sites of the different plant species. 2.4.1

Transplanting

Transplanting of perennial trees started on February 2016 followed by grasses, cotton plants and Ricinus communis. For the perennial tree species (Acacia ampliceps, Acacia nilotica, Casurina equisetifolia, Conocarpus lancifolius, Eucalyptus camaldulensis, Prosopis cineraria) planting spacing applied was 0.5 m, resulting in 30 planting stations per sub-block or 60 per block and 360 for the total six blocks for both irrigation methods (Table 3). For Acacia nilotica and Casurina equisetifolia, smaller number of plants was transplanted due to a shortage during the transplanting time (Table 3). For Distichlis spicata The International Desalination Association Conference on Water Reuse and Recycling – Nice, France


and Paspalum vaginatum, the number of plants in the flooding area was 326 and 516 per block, respectively, and in the sprinkler area 330 and 516 per block, respectively. For Cyamopsis tetragonoloba and Ricinus communis spacing was 3 m in both flooding and bubbler areas, resulting in 19 plants per row and for 4 rows per block the plants number is 76 per block (456 for the total of six blocks). 2.4.2

Seed sowing

Seeds for Salicornia bigelovii, Brassica napus, Cyamopsis tetragonoloba and Acacia ampliceps were sown directly on demarcated planting blocks of the research field. Acacia ampliceps seeds were first boiled and then immediately planted to increase the germination rate. Salicornia bigelovii and Brassica napus seeds were drilled in the marked rows and covered with a thin film of soil. Four seeds were planted at each plant station to increase the germination rate. After 4 weeks germination since planting, thinning was implemented on plant stations with more than one plant by removing other plants and leaving the healthiest one. Cyamopsis tetragonoloba was directly sown at each plant station in each row according to the recommended plant spacing. Plant spacing for Brassica napus was 0.5 m, thus, for each block 360 plants (90 plants per each one of the 4 rows per block) were planted in the flooding area (2160 in total). Under drip irrigation, 20 lines were installed per block with 90 plants per line, resulting in 1800 plants per block (10800 in total for the six blocks). For Salicornia bigelovii, plant spacing was 0.5 m in the flooding area, which results in 90 plants per row and for 6 rows per block the number of plants is 540 per block (3240 for the total of six blocks). Under the sprinkler area, plant spacing was 0.5 m, which gives 150 plants per row and for 9 rows per block the number of plants is 1350 per block (8100 for the total of six blocks). Table 1. Planting method and plant population for each plant species under different irrigation methods. Overhead irrigation

Plant species

Propagation Method

Flood irrigation

Bubbler

Sprinkler

Drip

Acacia ampliceps Acacia nilotica Casurina equisetifolia

Sowing Transplanting Transplanting

360¹ 360 360

360 240 210

-

-

Conocapus lancifolius Eucalyptus camaldulensis Prosopis cineraria

Transplanting Transplanting Transplanting

360 360 360

360 360 360

-

-


Transplanting Transplanting

1956 3096

-

1980 3096

-

Cotton spp Brassica napus Cyamopsis tetragonoloba

Transplanting Sowing Sowing

1056 2160 456

1320 456

-

10800 -

Ricinus communis Salicornia bigelovii

Transplanting Sowing

456 3240

456 -

8100

-



2.4.3

Plant establishing period

All plant species were irrigated during the establishment period with the WQ1, which has the lowest salinity. The establishment period lasted for 6 weeks after the completion of planting/sowing the different plant species. During the establishment period, dead plants were replaced with new ones in order to increase the establishment rate. Perennial plant species under the flood irrigation area were manually irrigated with well water during the plant establishment period. Manual irrigation was implemented with a water tanker truck through a 1-inch horse irrigation pipe of 60 meters length. The tanker truck moved on the constructed road next to each irrigation zone to be irrigated. Watering per each plant station was at least 2 L/day/tree. Sown seeds were irrigated through a hose pipe with a perforated end cap to avoid seeds being flushed away with the applied irrigation water. In the overhead irrigation area (bubbler, sprinkler and drip methods) WQ1 was applied through an automatic watering system. 2.5

Fertilization

Annual and perennial plant species require fertilization before planting as a basal application and continuous application at 6 and 8 weeks after planting, depending on the plant species. Top dressing application of urea and ammonium sulphate was implemented at 6 weeks after planting for Cotton spp, Cyamopsis tetragonoloba, Distichlis spicata, Ricinus communis and Paspalum vaginatum. Fertilizer application followed the required quantity per plant species. 2.6

Weather data

The weather data is daily recorded by a Davis Vantage Pro 2 weather station located at the NWTP camp. An Integrated Sensor collects the outside weather conditions by a Vantage Pro 2 console in 30-minute intervals. The weather station contains a rain collector (self-emptying tipping-bucket), temperature sensor (Platinum wire thermostat), humidity sensor (Film capacitor element), an anemometer (vane anemometer with wind cups) and a solar radiation sensor. The data is recorded by a USB Data Logger and is thereafter readout by DAVIS software WEATHER LINK. The data is downloaded off the weather station at the beginning of each month. Monthly average air temperature, humidity, wind speed, solar radiation and rainfall are calculated from the available data. Figure 9 shows the Davis Vantage Pro 2 weather station located at the NWTP camp. 2.7

Evaporation rate

Class A pan provides a measurement of the combined effect of temperature, humidity, wind speed and sunshine on the reference crop evapotranspiration (ET). Three Class-A evaporation pans (d = 1 m; height = 0.3 m) are installed in the BARP field at different locations near the outlets of the three different water qualities. Water is filled up to 200 mm depth with each water quality and allowed to evaporate for 24 hours. Water depth measurements are taken every morning before 9 am from an installed graduated ruler in the pan. After recording the daily evaporation rate (in mm), the class A pan is refilled to 200 mm. 2.8

Flow rate

Doppler instrument equipped with a clamp-on ultrasonic sensor, a connecting cable and an electronic monitor is mounted on PVC main pipe at a convenient location near the electrical power source (i.e., a The International Desalination Association Conference on Water Reuse and Recycling – Nice, France


generator). It is used to record the instantaneous daily flow rate on each line when the pump is operating. Daily generator running hours are also recorded each WQ. In that way, the daily flowrate of each WQ send to the BARP can be calculated. 2.9

Water quality

Water sampling and analyses started on March 2016. WQ1, WQ2 and WQ3 are monitored on a biweekly basis. Two samples are collected from each water quality location using 400 mL glass and polyethylene bottles respectively, resulting in a total of 6 samples per sampling campaign. All water quality parameters measurements are performed at the NWTP laboratory. Measurement of pH is performed using a calibrated WTW P4 portable instrument with a pH probe. Conductivity is measured using a conductivity probe and dissolved oxygen using an ORP probe connected to HQd meter. 2.10

Soil sampling

Soil sampling aims to determine the salt accumulation within the root zone of the plant species caused by the irrigation of each WQ. Initial samples were collected prior to the planting and irrigation. A series of samples in the middle assessment row were taken by collecting three sub-samples per irrigation block, and then mixed to a composite sample for each irrigation block. A total of 12 samples represent all irrigation blocks. Soil sampling will occurs every year after the commissioning period. The next sampling is scheduled on February 2017. 2.11

Plant monitoring

Germination rate of sown plant species, i.e., Brassica napus, Cyamopsis tetragonoloba, Salicornia bigelovii and Acacia ampliceps, were determined at 4 weeks after planting by germination counting. Germinated plants were counted per each plant station and recorded per each irrigation block. Plant establishment assessment was performed at 2, 4 and 6 weeks after planting. The total numbers of live and dead plants were counted on every block and recorded for each transplanted and germinated plant species.

III.

RESULTS

The research and monitoring phase of the project started 2 weeks after planting. Water balance, water quality, soil quality and plant monitoring are investigated according to the schedule presented in the following Table 4. 5Weather data for the first operational months of the BARP are presented in Table 5. As this table shows, high temperature values occurred during the plant establishment period over the last two months, while no rainfall incidents took place. Table 6 presents water quality results after the first laboratory analysis for water temperature, pH, conductivity, boron, OiW and. Figures here represent average values after the first four sampling dates, i.e., 21st March, 7th April, 20th April and 9th May.



Table 4. Monitoring schedule for the different tasks during the project period. Monitoring task

Frequency

Water flow rate Water quality Soil quality Plant parameters Perennial plants Annual plants Leaf sampling (all plants)

Daily Bi-weekly Every year

Dry weight (annual grasses)

Every three months

Every three months Every four weeks Every six months

Table 5. Weather data during the plant establishment period. March

April

May

Parameter Air temperature [°C]

mean

max

min

mean

max

min

mean

max

min

26.7

39.9

15.5

28.8

43.2

17.7

31.6

44.4

21.7

Relative humidity [%]

64.9

97.0

8.0

51.1

96.0

7.0

59.1

96.0

4.0

Pressure [hPa]

758

1014

754

1008

1017 1002

1004

1009

997

Wind velocity [m/s]

6.0

13.4

0.0

4.6

11.2

5.1

10.7

0.0

250.2

0.6 961. 0 17.5

0.0

245.2

9.5

11.6

0.0 951. 0 20.0

Total rainfall [mm] Solar radiation [W/m²] Evaporation [mm/d]

12.3

0.0

0.0 0.0

257.2

937.0

0.0

5.0

15.9

17.0

14.0

Table 6. Mean (± standard deviation) values of water quality parameters (n=4). Parameter

WQ1

WQ2

WQ3

Water temperature [°C]

27.6 ± 4.1

27.9 ± 4.3

28.5 ± 4.5

Water pH

7.7 ± 0.2

7.9 ± 0.3

8.2 ± 0.2

Water conductivity [mS/cm]

12.8 ± 0.4

13.4 ± 0.4

14.9 ± 0.7

Oil in water [mg/L]

1.3 ± 0.2

0.5 ± 0.2

0.1 ± 0.0

Boron [mg/L]

4.7 ± 0.3

5.1 ± 0.4

5.7 ± 0.2

Table 7 below summarizes the germination rate of each plant species 4 weeks after planting.



Table 7. Germination rate of annual plant species in both flood and overhead irrigation blocks at 4 weeks after planting. Overhead irrigation Bubbler Sprinkler Drip P G %G P G %G P G %G P G %G 360 0 0 360 0 0 2160 1291 60 - 10800 2420 22 Flood irrigation

Plant species Acacia ampliceps Brassica napus Cyamopsis 456 340 75 456 50 11 tetragonoloba Salicornia bigelovii 3240 0 0 - 8100 0 P = planted, G = germinated, %G = germination rate (percentage)

-

-

-

-

0

-

-

-

Cyamopsis tetragonoloba had the highest germination rate followed by Brassica napus in the flood irrigation area. No germination was recorded for Acacia ampliceps and Salicornia bigelovii. Salicornia bigelovii seeds were irrigated with WQ1 (salinity of 7.5 mg TDS/L), while Brassica napus and Cyamopsis tetragonoloba seeds were manually irrigated with well water (salinity of 3.2 mS/cm), which could have affected plant germination. Germination rate in the overhead irrigation blocks was lower than the flood irrigation blocks for Cyamopsis tetragonoloba and Brassica napus. As for the flood irrigation blocks, no germination was recorded for Acacia ampliceps and Salicornia bigelovii. All the directly seeded plant species in these blocks were irrigated with WQ1 (salinity of 12.8 mS/cm). After 2 weeks of irrigating with well water, live and dead plants for the perennial plant species under flood irrigation were counted and establishment rate was determined and recorded. The same procedure of monitoring was also repeated at 4 and 6 weeks after planting on the same plant species under flood irrigation with water of WQ1. Table 8 presents the establishment rate for all plant species during the last monitoring campaign (i.e., 6 weeks after planting). The results showed that Eucalyptus camaldulensis and Conocarpus lancifolius have the highest plant survival rate (99%) under flood irrigation method. Acacia nilotica showed the lowest survival rate (75%). In general, establishment rates for all perennial trees under flood irrigation are very good. Under bubbler irrigation method, Conocarpus lancifolius had again the highest plant survival rate (99%). Good establishment rates were also recorded for Eucalyptus camaldulensis and Casurina equisetifolia. Lower rates, but still encouraging for the study were recorded for Acacia nilotica (55%) and Prosopis cineraria (45%). Annual plant species and grasses (i.e., Distichlis spicata, Paspalum vaginatum, Cotton spp., Brassica napus, Cyamopsis tetragonoloba and Ricinus communis) were also counted using the same procedure of recording live and dead plants. Table 10 presents the results for these plant species, while Figure 11 shows the establishment rate variations at 2, 4 and 6 weeks after the planting. The two grasses (Distichlis spicata and Paspalum vaginatum) showed the highest survival rates under flood irrigation (94% and 100%, respectively), a trend which was maintained during all three monitoring campaigns. However, under sprinkler irrigation method, only Paspalum vaginatum managed to maintain a high establishment rate (100%); Distichlis spicata survival rate was only 14% under this irrigation method. Cotton showed good survival rates under both irrigation methods: 80% for flood irrigation and 76% for bubbler irrigation. The rest species (Brassica napus, Cyamopsis tetragonoloba and Ricinus communis) showed very low or low establishment rates. The first two were sown only after 4 weeks since planting and their survival rapidly decreased at 6 weeks after planting, for both irrigation methods (flood and overhead). Ricinus communis did not manage to establish under the specific conditions of the project. The International Desalination Association Conference on Water Reuse and Recycling – Nice, France


Table 8. Establishment rate of all plant species at 6 weeks after planting. Flood irrigation

Overhead irrigation Bubbler Sprinkler P E %E P E %E 240 132 55 210 182 87 360 358 99 -

Drip P E %E -

P E %E Plant species Acacia nilotica 360 269 75 Casurina equisetifolia 360 297 83 Conocarpus lancifolius 360 358 99 Eucalyptus 360 358 99 360 341 95 camaldulensis Prosopis cineraria 360 327 91 360 163 45 Distichlis spicata 1980 1867 94 - 1980 276 14 Paspalum vaginatum 3096 3085 99 - 3096 3058 100 Cotton spp 1056 847 80 1320 1005 76 Brassica napus 2160 326 15 - 10800 814 Cyamopsis 456 48 11 456 11 2 tetragonoloba Ricinus communis 456 4 1 456 0 0 P = planted, E = established, %E = Establishment rate (percentage) V.

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CONCLUSIONS, RESULTS, OR SUMMARY

Flood irrigation method seems so far to favour plant establishment. Perennial tree species under flood irrigation present the highest survival rates, higher compared to those under bubbler irrigation method. Regarding all perennial tree species, the outcome is positive and the survival rates after the first 6 weeks after planting ranged were good, ranging between 60% - 90%. The only exception in this category is Acacia ampliceps, which did not manage to survive. Annual grass species (i.e., Paspalum vaginatum and Distichlis spicata) established well under flood and bubbler irrigation method (establishment rates up to 99%). Distichlis spicata showed a low establishment rate only under bubbler irrigation (14%). Cotton plants also present good establishment rates under both irrigation methods (flood and bubbler). However, the rest of the annual species, i.e., Brassica napus, Cyamopsis tetragonoloba, Ricinus communis and Salicornia bigelovii present a negative overall outcome under both flood and overhead irrigation methods, with very low survival rates or no survival at all. In general, so far only the following plant species present challenges to establish under the experimental conditions: Acacia ampliceps, Brassica napus, Cyamopsis tetragonoloba, Ricinus communis and Salicornia bigelovii. Future tasks and experiments will be carried out to determine the limiting factor of the germination/plant establishment (i.e., water salinity). Moreover, a second planting campaign will start after the summer months, in order to evaluate the potential improvement (or not) of the survival rates for the plant species with low establishment, when planted under autumn conditions.



VI.

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ACKNOWLEDGEMENT

It is acknowledged that the current project is co-funded and supported by PDO.

