PHD dissertation summary Land and water environment: Using wastewater from intensive catfish pond for irrigating paddy field

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Objectives of the study: Assessing the situation of catfish farming in some areas of the Mekong Delta as a basis for proposing measures to manage waste from catfish ponds; the survey and analysis in catfish ponds to assess the composition and characteristics; assessing the pollutants load of waste water from catfish ponds; assessing the possibility of wastewater treatment from catfish ponds and benefits of environmental when using wastewater for irrigating paddy fields.

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MINISTRY OF EDUCATION AND TRAINING CAN THO UNIVERSITY PHD DISSERTATION SUMMARY Land and water environment Code: 62 44 03 03 DANG QUOC CUONG USING WASTEWATER FROM INTENSIVE CATFISH POND FOR IRRIGATING PADDY FIELD Can Tho, 2015
WORKS TO BE DONE IN CAN THO UNIVERSITY The scientific guidance: Assoc. Prof. Dr. Truong Thi Nga The thesis will be defend against the council state dissertation meeting at the: At time day month year Reviewer 1: Reviewer 2: Dissertation can be found at: Learning resource center of Can Tho University. National library of Vietnam.
LIST OF PUBLISHED WORKS 1. Dang Quoc Cuong, Truong Thi Nga and Tran Thi Diem Phuc, 2014. Effects of using rice fields to treat polluted water of catfish (Pangasianodon hypophthalmus) pond. Journal of science, Can Tho University. No 3. ISSN 1859-2333. 2. Dang Quoc Cuong and Truong Thi Nga, 2015. Improvement of water quality by utilizing wastewater from catfish ponds for rice field irrigation. Reasoning, science and business journal of the Ministry of Natural Resources and Environment. No. 1+2 (2015). 53-55 pages. ISSN 1859-1477. 3. Dang Quoc Cuong, Truong Thi Nga and Nguyen Thi Kim Dung, 2015. Amelioration of nitrogen, phosphorus from wastewater of intensive fish ponds by rice fields. Journal of science, Can Tho University. Part A: Science, Technology and Environment: 39 (2015): 66-70. ISSN 1859- 2333. 1
Chapter 1 INTRODUCTION 1. The Urgency of Dissertation The Mekong Delta (MD) is a key region for aquaculture and processing export seafood, bringing many benefits to the economy and society. Catfish farming area of the Mekong Delta in 2014 was estimated at more than 5.500 hectares with production of 1.116 thousand tonnes (Ministry of Agriculture and Rural Development, 2014). In addition, the operations of aquaculture still exist shortcomings. Wastewater in aquaculture was discharged directly into the environment without external treatment. This problem was not only affects in a farming area but also affects other neighborhoods. The results of previous studies showed in wastewater intensive catfish ponds containing high nutrients, can be reused. The dissertation "Using wastewater from intensive catfish pond for irrigating paddy field" was implemented with the purpose to recycle nutrients in wastewater from catfish ponds for irrigating paddy, reduce inorganic fertilizer and contribute to reduce the water pollution. 2. Objectives of the study - Assessing the situation of catfish farming in some areas of the Mekong Delta as a basis for proposing measures to manage waste from catfish ponds. - The survey and analysis in catfish ponds to assess the composition and characteristics. - Assessing the pollutants load of waste water from catfish ponds. - Assessing the possibility of wastewater treatment from catfish ponds and benefits of environmental when using wastewater for irrigating paddy fields. 3. Subjects and scope of research Wastewater from intensive catfish ponds in Vinh Thanh and Thanh My district, Can Tho city, soil of paddy fields and rice surrounding households were selected as study subjects to assess the potential to reduce pollution from intensive catfish pond in each stage of development of paddy fields. The survey assessed the current state of catfish, the composition and characteristics of wastewater from catfish ponds in the five distriscts are: Vinh Thanh (Can Tho), Thanh My (Can Tho), Long Ho (Vinh Long), Hong Ngu 2
(Dong Thap), Chau Thanh (An Giang) to assessing the quality of wastewater catfish ponds in the area of intensive research. The experiments using wastewater for irrigating paddy fields was conducted in winter-spring and summer-autumn from 2013 to 2015 in Vinh Thanh, Can Tho on Jasmine rice (105 days) and OM 6976 (90 days) in order to determining the potential to reduce pollution and increase nutrients of rice. The experimental models using wastewater for irrigation farming ponds on paddy fields in Hong Ngu (Dong Thap), Chau Thanh (An Giang) and Long Ho (Vinh Long) to assessing research results outside the practice. 4. The content of study Surveying the current state of intensive catfish in some provinces of Mekong Delta are: An Giang, Vinh Long, Can Tho and the composition, properties of wastewater from catfish ponds in some key areas are: Dong Thap, An Giang, Vinh Long and Can Tho. Assessing the pollution load of COD, total nitrogen, total phosphorous from the catfish intensive ponds in Vinh Thanh, Can Tho. Reseaching the role of paddy fields which in reducing the contamination of organic matter, nitrogen, phosphorus from the catfish intensive ponds in the stages of growth and development of paddy. 5. Structural dissertation content The dissertation is structured into 5 chapters: Chapter 1: Introduction; Chapter 2: Literature review; Chapter 3: Research methodology; Chapter 4: Result and Discussion; Chapter 5: Conclusions and suggestions. 6. The practical significance of the dissertation - Results of research show that if irrigating paddy combined with give 2/3 NPK will be the highest paddy yield and profits. - Results of research show that the possibility of scaling up the use of paddy fields to wastewater treatment catfish ponds in areas with catfish activity and rice cultivation, contributing to protect the water environment. - This is a scientific basis for further studies on reusing of wastewater catfish ponds to subjects other crops. Results of the dissertation can be implemented and applied in practice in the Mekong Delta and other provinces have similar conditions. 3
7. The novel of dissertation - Assessing the ability to provide nitrogen, phosphorus of wastewater from catfish ponds in the study area, in particular it can reduce 1/3 of chemical fertilizers without affecting yield. - Results of the dissertation assessed the ability waste treatment when using wastewater from catfish ponds for paddy fields through the process absorbing nitrogen, phosphorus; accumulation of biomass; the nitrogen, phosphorus were accumulated the most on the parts ground when the plant growth after 12 weeks of the experiment. - The reduction of the concentration pollutants in wastewater from catfish ponds was due to use organic matter for paddy, but concurrent shows the role of paddy soil are treatment of pollutants from catfish ponds, contribute to reducing the eutrophication of paddy soil by causing pollutants. - The application of the fact shows the possibility of scaling up using paddy fields for treatment wastewater from catfish ponds in areas have activity catfish and paddy cultivation, contribute to protecting the water environment. Chapter 2 LITERATURE REVIEW 2.1 The scientific basis of the dissertation The research utilizing waste in general and waste in the particular of the fisheries sector for agricultural purposes was a necessary goal in the world as well as in Vietnam where the Mekong Delta in specific. In fact, intensive catfish form has a major impact on the environment due to excess feed, feces and accumulated excrement in water (Cao Van Thich, 2008). According to Nguyen Phan Nhan (2011), in one season with the fish farming area was 5181.5 m2, density was 53 individual/m2, the total amount of food provided was 197.750 tonnes, then discharged was 191.37 tons of COD; 50.11 tons TKN and 16.55 tons TP. The study of Phan Thi Anh et al., (2010), producing 1 ton of catfish was emissions 200.9 kg BOD; 246.6 kg COD; 557.1 kg TSS; 36.5 kg 9.1 kg of nitrogen and phosphorus. Thus, the estimated production of catfish in Mekong Delta 2014 is discharged 275,205.6 tons (COD), 40,734 tonnes (N) and 10,155.6 tons (P). Wastewater from catfish ponds with nutrient and organic matter, necessary for the development of paddy. Therefore, utilizeing nutrients in wastewater from catfish ponds provided the process development of paddy, to reduce the amount of chemical fertilizers used and limited pollution of surface water. 4
Tran Duc Ha (2003) said the sewage filtration through the soil, the suspended particles and colloids was trapped in the top layer. Those which make up the lining consists of a multitude of microorganisms which have capable of absorption and oxidation of organic substances in wastewater. According to Luong Duc Pham (2002), the irrigation fields has 2 functions: Wastewater treatment and watering fertilizer plant. For the agriculture irrigated fields, it can make soil moisture and to satisfy the nutrients (N, P, K) for crops. The using wastewater for irrigating plant can increase the productivity up to 2-4 times. In the process of irrigation, crops use a part of the nutrients in wastewater, 49% for nitrogen, phosphorus and potassium can be up to 90%. The rest are in land and in water exit channel. The wastewater treatment by irrigated fields and wet landcan achieve very high efficiency: BOD20 was 10- 15 mg/L, 25 NO3 mg/L, decreased to 99.9% of bacteria. Water after treatment without disinfectant can pour into waterways. 2.2 The situation of catfish (Pangasius hypophthalmus) According to The ratification of planned breeding, catfish processing in Mekong Delta region by 2020, the development of aquaculture, catfish processing sector in Mekong Delta become the important economic of Vietnam's seafood according to direction the industry and environmental friendliness. With the targets to 2016, the surface water catfish area is 5,300- 5,400 ha, yields 1,250,000-1,300,000 tons; to 2020, the surface water catfish area is 7,600-7,800 ha and output is 1.8 to 1.9 million tons. This development creates profits and income, it can also cause harmful and adverse environmental impacts such as pollution or change the biodiversity (Pullin, 1993 and Tovar et al., 2000). 2.3 Characteristics of the water environment in intensive catfish ponds According to Giang et al. (2008), in the water of fisheries pond include ammonia nitrogen (TAN), NO2, and phosphorus (PO43-), biochemical oxygen demand (BOD), COD and H2S are higher the concentrations allowed. However, the intensive farming model contains very large the concentrations of nitrogen (TN), phosphorus (TP) and organic matter are the main factors causing environmental pollution (Schwartz and Boyd, 1994; Hakanson et al. , 1988; Lemarie et al., 1998 cited in Schneider et al., 2005). The study by Boyd (1985) showed that catfish absorb only 27-30% nitrogen and 16-30% phosphorus and 25% of organic matter into the food. Research by Phan Thi Cong et al. (2009) showed that wastewater and sludge ponds containing high amounts of nutrients (NH4-N, P, K, Ca and Mg). 5
Wastewater and sludge ponds had levels of heavy metals (As, Hg, Pb) and Cu and Zn is very low or undetectable; The residual of chlorine compounds and organic phosphorus undetectable. 2.4 Overview of reusing wastewater for farming catfish Characteristic of wastewater, it was easily biodegradable in case of fish production areas located in rural areas, therefore solutions for wastewater treatment from fish farming are inclined towards using natural biotechnology, simply (Duong Cong Chinh et al., 2010). Paddy consume a large volume of water when fully watered, especially during the dry season. If wastewater from nearby ponds can provide most of the water demand for paddy and also provides a significant amount of nutrients (Van Phung Cao et al., 2010). The system combines aquaculture and agriculture has proved more practical in terms of technical, social and environmental sustainability (Huat & Tan, 1980 cited in Chau Thi Da et al., 2012). Research of Cao Van Phung was conducted in 2008-2009 the dry season in Phu Tan district, An Giang province for resulting the plots in high-yield rice cultivation as well as the absorption of nutrient (the macro elements and secondary) high in straw and grain (kg/ha) except for the phosphorus in straw. Results showed that the combination of aquaculture into rice farming systems can reduce surface water pollution, reduce chemical fertilizer use in the field. Especially in the waste water from the catfish pond with the nutrients needed for the development of the rice. It can thus be increase profits for farmers while contributing to the development of sustainable the agriculture in addition to protecting the environment. However, if farmers do not reduce the amount of fertilizer N when using reusing of wastewater, the risk of falling paddy will be increased (Phung et al., 2009). Chapter 3 RESEARCH METHODOLOGY 3.1 Surveying research of the current catfish state in the Mekong Delta and composition, nature of wastewater catfish ponds in the study area 3.1.1 Collecting information and water sampling some key farming area in the Mekong Delta as Vinh Long, Can Tho and An Giang Investigation, collecting secondary data from the provincial authorities, district and related to agricultural production in order to collect information relating to the current state of the area, production, policies, regulations development plans, the development potential and the obstacles are encountered in Vinh Long, Can Tho and An Giang. Interviewed 50 households have intensive 6
catfish in Vinh Thanh District - Can Tho by questionnaire in order to grasp the issues related to forms of production, technical issues, and the business environment. 3.1.2 Survey parameters for composition and properties of wastewater catfish ponds in the study area Based on the production process and change the water of catfish farmers will be sampling carried out over time farming: Phase 1 (50-70 days), Phase 2 (100-120 days), Phase 3 ( 150-170 days). Water samples were collected at the drain discharge when the water exchange. 3.2 Assessmenting the pollution load COD, total nitrogen and total phosphorus in catfish ponds The method was applied to calculate the pollution load due catfish activity in the study area with Circular No. 02/TT/2009/BTNMT, the pollution load was calculated based on the concentration of pollutants and largest wastewater flow. Some major pollutants of catfish farming activities are monitored as COD, total nitrogen and total phosphorus. The pollution load was calculated through pond water quality. 3.3 Research on the role of paddy rice soil in reducing organic pollutants N, P in wastewater catfish ponds 3.3.1 Experiment 1: Research in small-scale The experiment was performed in summer-autumn crop in Thanh My, Vinh Thanh, Can Tho. All treatments were constructed in the randomly blocks design including 4 treatments and 3 replicates. T1: Using river water to irrigate paddy rice and apply NPK (90N - 50P2O5 - 30K2O); T2: Using wastewater to irrigate paddy rice and apply NPK (90N - 50P2O5 - 30K2O); T3: Using wastewater to irrigate paddy rice and apply 2/3 NPK (90N - 50P2O5 - 30K2O); T4: Using wastewater to irrigate paddy rice and apply potassium (30K2O). 3.3.2 Experiment 2: The study in the summer-autumn crop The experiment was performed in summer-autumn crop, all treatments were constructed in the randomly blocks design in Thanh My, Vinh Thanh, Can Tho. The experiment consists of 4 treatments and 3 replicates. T1: Using river water to irrigate paddy rice and apply NPK (90N - 50P2O5 - 30K2O); T2: Using wastewater to irrigate paddy rice and apply NPK (90N - 50P2O5 - 30K2O); T3: Using wastewater to irrigate paddy rice and apply 2/3 NPK (60N - 30P2O5 - 20K2O); T4: Using wastewater to irrigate paddy rice and apply potassium (30K2O). 7
3.3.3 Experiment 3: The study in the winter-spring crop The experiment was constructed in the randomly blocks design in Vinh Binh, Can Tho. The experiment consists of 4 treatments and 3 replicates: T1: Using wastewater to irrigate land fields (no paddy rice); T2: Using wastewater to irrigate paddy fields (no fertilizer); T3: Using wastewater to irrigate paddy rice and apply NPK (60N - 40P2O5 - 40K2O); T4: Using wastewater to irrigate paddy rice and apply NPK (90N - 60P2O5 - 60K2O). 2 3 1 Figure 3.1 The experiment was arranged in the crate (1), in the summer-autumn crop (2) và on the winter-spring crop (3) 3.4 The building model using wastewater for irrigating paddy rice file The building model using wastewater for irrigating catfish ponds in paddy fields is done in the summer-autumn paddy rice crop, the experimental consists of 5 fields have received wastewater from ponds and 5 fields have not other received wastewater at: Thanh My, Vinh Binh, Vinh Thanh-Can Tho; Hong Ngu-Dong Thap; Chau Thanh-An Giang and Long Ho-Vinh Long. T1: Using river water to irrigate paddy rice and apply NPK (90N - 50P2O5 - 30K2O); T2: Using wastewater to irrigate paddy rice and apply NPK (60N - 30P2O5 - 20K2O) Chapter 4 RESULTS AND DISCUSSION 4.1 Status of catfish in the Mekong River Delta (MRD) and the components, properties wastewater catfish ponds in the study area 4.1.1 The composition and properties of wastewater from catfish ponds in some key areas of the Mekong Delta The results of the survey was presented in Table 4.1. 8
Table 4.1 The average of the components and properties of the wastewater catfish ponds in a number of key areas in the Mekong Delta DO COD TKN TP Location pH (mg/L) (mg/L) (mg/L) (mg/L) Hong Ngu – Dong Thap 7.20±0.04 3.86±0.19 59.03±7.85 11.85±0.47 3.40±0.18 Chau Thanh – An Giang 6.78±0.21 4.68±9.52 76.33±12.27 7.22±0.17 1.88±0.11 Long Ho – Vinh Long 7.04±0.08 4.01±0.69 66.73±13.20 9.84±0.51 2.89±0.21 Vinh Thanh – Can Tho 6.97±0.19 4.12±0.44 80.66±1.40 11.23±0.08 1.76±0.35 NTR 08:2015/BTNMT (column B1) 5.5 – 9 ≥4 30 - - Note: Average±deviation; Data were collected at the end crop (when catfish are 5-6 months old) Table 4.1 shows that the levels of nutrients such as COD, TKN and TP in ranging from 59.03 mg/L±7.85 to 80.66 mg/L±1.40, 7.22 mg/L±0.17 to 11.85 mg/L±0.47 mg/L and 1.76 mg/L±0.35 to 3.40 mg/L±0.18, respectively. Compared with NTR 08: 2015/BTNMT (column B1), COD was higher than norms 2-3 times. Wastewater from catfish ponds have higher nutritional content than regulations. So, wastewater should be treated before being discharged into the receiving environment. 4.1.2 Current status and the composition and the properties of water- intensive catfish ponds in the study area 4.1.2.1 Status of catfish farming in the study area Through interviewing 50 households which are intensive catfish cultivation in Vinh Thanh, Can Tho shows catfish period lasts from 6-12 months. The average stocking density was about 42 individual/m2, while the lowest density was 30 individual/m2 and the highest was 81 individual/m2, the average size is 30 individual/kg. Around 90% of catfish farming was interviewed has the stocking density less than 50 individual/m2. 100% of catfish farmer has no wastewater treatment pond before discharging into the water body. 9
Table 4.2 The results of the interview of 50 households in Vinh Thanh district Number of Area (ha) households Percent (%) 0.1 – 0.5 15 30 0.5 – 1.0 30 60 > 1.0 5 10 Time 6 months - 8 months 30 60 8 months - 12 months 20 40 2 Density (individual/m ) ≤ 50 45 90 > 50 5 10 The average size of farming was 30 individual/kg The depth ranges from 3.4 to 4 m The frequency of water changes: in January and February the number of times water changes was 3-5 days /times (rate from 20 - 40%); from March onwards the number of times water changes was daily (rate from 50-70%) Wastewater treatment No treatment 45 90 Irrigating for paddy field 5 10 Sludge treatment: 100% of households pumped the sludge into the pond empty, to fill or vegetable stew faint or grow grass Sludge removal from 5-10 times/season Food use: 100% industrial food Frequency of feeding 2 times/day 40 80 1 timea/day 10 20 Water use to pumpe into catfish ponds: using 100% channel water and water was no treatment before pumping into the pond Pond treatment before starting a new season: 100% of households using lime +salt The average yield 322.5 tons/ha/crop, the average range to 230-410 tonnes/ha 100% of household was no treatment wastewater before discharging it into the environment 100% of households used the food industry. With the frequency was 2 times/day (about 80%) and the frequency was 1 times/day (about 20%). The survey shows that the most of the farmers are not interested in technical feeding, which them feeding when fish no feed then they stop, this cause was the pollution to the pond by feed wastage besides it would also push up the cost of higher. Regarding management water ponds, 100% of households used to water of channels pumping into the pond without treatment, the frequency of water changes of the households as follows: in January and February the 10
number of times water changes was 3-5 days /times (rate from 20 - 40%); from March onwards the number of times water changes was daily (rate from 50-70%). In the opinion of the households, the frequency of water was every day so that increasing the rate growth of fish and meat quality. The frequency of sludge usually pump between 5-7 times/crop. 100% of households were pumping sludge into empty pond, to fill or grow vegetables stew faint or grow grass. The pumping sludge in crop were improving water quality in the pond. Table 4.3 Evolution of the chemical composition of wastewater intensive catfish ponds in Vinh Thanh district over time DO COD TKN TP Fish time (day) pH (mg/L) (mg/L) (mg/L) (mg/L) 50 7.36b±0.07 3.72de±0.21 45.33e±4.62 8.59e±0.32 0.84e±0.03 60 7.38b±0.17 3.77cde±0.12 53.33d±0.00 8.96d±0.00 0.92e±0.03 70 7.75a±0.06 4.22cd±0.13 65.18c±5.13 9.33d±0.32 0.94e±0.01 100 7.16cb±0.19 4.28c±0.37 78.58ab±4.99 9.08d±0.29 0.94e±0.03 110 7.06cd±0.08 4.05cd±0.09 74.43b±3.46 9.82c±0.25 1.28de±0.11 120 6.67e±0.29 4.12cd±0.49 82.56a±0.67 9.11d±0.11 0.90e±0.02 150 6.66e±0.02 3.30e±0.07 78.24ab±1.26 11.48a±0.16 1.87c±0.08 160 6.82de±0.12 3.95cd±0.18 80.68a±2.42 10.84b±0.15 1.62bc±0.60 170 6.97cd±0.19 4.12cd±0.44 80.66a±1.40 11.23a±0.08 1.76c±0.35 NTR 08:2015/BTNMT 5.5 – 9 ≥4 30 - - (column B1) Note: In the same column if letters are different (a-b-c-d-e) with statistical significance (5%, Duncan). Nutrient content in catfish ponds were gradually increasing to the end of the period, although the frequency of water changes were also increased. Over time farming, the levels of food were increased, fish bigger were increase in food use. Thus, the end of the crop, the fish is the bigger, the nutrition needs higher, the food provides as much, they increase the risk of pollution. Wastewater in catfish ponds have contain nitrogen, phosphorus higher NTR 08:2015 (column B1), if they were discharged directly into the environment which would cause pollution. 4.2 The loading of COD, total nitrogen and total phosphorus in catfish ponds Wastewater flow in ranging from 0.378 to 0.594 m3/s is always higher than the water flow level was 0.146 to 0.316 m3/s. The average of the load COD, TKN and TP of intensive catfish ponds to increase over time in ranging from 1.90 to 5.37 tonnes/ha/day; 0.19 to 1.46 tonnes/ha/day and from 0.01 to 0.53 tonnes/ha/day, respectively. The reason was that increasing the amount of feed used at the end of season. The loading of COD, TKN and TP were 533.67 11
tonnes/ha/crop; 148.33 tonnes/ha/crop and 44.50 tonnes/ha/crop, respectively. This suggests that, wastewater from catfish ponds have containing high levels of nitrogen and phosphate, can be used to irrigate for paddy fields. 4.3 Role of the paddy fields in reducing pollution of organic matter, nitrogen, phosphorus in wastewater from catfish ponds 4.3.1 Quality of paddy soild before and after using wastewater from catfish ponds in the summer-autumn paddy crop According to the rating scale, the average soil pH in the experiment was 4.85, it was considered at the low, the average electrical conductivity soil EC was 679 (µS/cm) was not affect the plant. The average composition of organic matter in soil was 6.37% on the average. The average total nitrogen N was 0.3%, it was considered at the average, the average N-NH4+ was 23.74 (mg/kg), it was considered at poor and the average NO3-N was 0.173 (mg/kg) at low. The average total soil phosphorus was 0.058 (% P2O5) on the average, leads to the average phosphorus was 11.52 (mgP2O5/kg), it was considered at the average (Ngo Ngoc Hung, 2009). Table 4.4 The average of physical, chemical of paddy rice soil before the experiment Soil before The phase of soil (80 day) Values the Case 1 Case 2 Case 3 Case 4 experriment pH 4.85±0.01a 4.55±0.08b 4.63±0.06b 4.67±0.04ab 4.82±0.19a a c bc bc EC (µS/cm) 679±2.65 403±17 420±27 431±12 440±19b CHC (%) 6.37±0.04abc 6.13±0.11c 6.73±0.06a 6.55±0.28ab 6.33±0.29bc Total N (%) 0.30±0.02 0.28±0.01 0.29±0.02 0.31±0.01 0.30±0.01 N-NH4+ (mg/kg) 23.74±0.09 23.10±1.31 24.89±1.18 24.54±1.42 23.18±1.66 N-NO3- (mg/kg) 0.17±0.01a 0.05±0.01c 0.08±0.01b 0.07±0.01c 0.06±0.01c Total N (%P2O5) 0.06±0.00bc 0.05±0.00d 0.07±0.00a 0.06±0.00ab 0.05±0.00cd Phosphorus 11.52±0.09ab 10.95±0.47bc 11.99±0.66a 11.66±0.23ab 10.27±0.25c (mgP2O5/kg) Notes: In the row at the cases, if letters (a-b-c-d) are different with statistical significance (p
4.3.2 The ability reduce wastewater catfish ponds of paddy field in the summer-autumn crop in 2013 The values are pH; DO; turbidity; EC in wastewater catfish ponds after through paddy fields ranging from 4.11±0.04 to 5.18±0.73; 3.11 mg/L±0.79 to 4.10 mg/L±0.50; 25.2 NTU±4.1 to 44.3 NTU±3.3; 1,025 μS/cm±77 to 2,278 μS/cm ± 292, respectively. 4.3.2.5 The concentration of COD (mg/L) of waste water after treated by paddy field COD of wastewater had reduced between before and after going through all of treatment. Almost of outlet COD was lower than NTR 08:2015/BTNMT B1 column at seeding, tillering and booting. Table 4.5 COD of wastewater from catfish pond after treated by paddy field NTR COD (mg/L) 08:2015/B Stage Wastewater NPK 2/3 NPK K TNMT of catfish supplement supplement supplement (column pond treatment treatment treatment B1) Seeding 45.3±4.6a 27.4±4.1b 26.6±4.5b 27.3±2.9b Tillering 53.3±0.0a 27.5±0.6b 23.5±0.4c 18.9±0.2d Booting 65.2±5.1a 33.8±2.8b 27.7±1.8c 22.2±1.8c 30 Flowering 78.6±5.0a 39.8±4.5b 34.0±3.9bc 29.2±3.5c Fruiting 82.6±0.7a 36.2±0.7b 33.2±0.7c 32.6±0.7c Note: On the same row, the different characters (a-b-c) gave the significant difference (5%, Duncan). On NPK supplement treatment, there was difference between before and after going through paddy field from 17.9 mg/L at the seeding stage to 46.3 mg/L at the fruiting stage; On 2/3 NPK supplement treatment was from 18.8 mg/L to 49.4 mg/L and from 18 mg/L to 50 mg/L for the treatment of K supplement only. Rice was more growth, the pollution reduction ability of catfish pond wastewater was higher. 4.3.2.6 The concentration of TKN (mg/L) of wastewater after treated by paddy field At the treatment of catfish pond waste water only, TKN value fluctuated around lowest at 1.49 mg/L±0.32 on the condition of K supplement treatment and highest at 5.55 mg/L±0.32 on the treatment of NPK supplement. There was statistic meaning difference (5%) between before and after going through paddy field for TKN. 13
Table 4.6 TKN of catfish pond waste water after treated by paddy field TKN (mg/L) Waste water Stage NPK 2/3 NPK of catfish K supplement supplement supplement pond treatment treatment treatment treatment Seeding 8.59±0.32a 5.55±0.32b 5.51±0.25b 5.39±0.16b Tillering 8.96±0.00a 4.11±0.32b 3.55±0.32c 2.05±0.32d Booting 9.33±0.32a 2.61±0.32b 2.05±0.32bc 1.49±0.32c Flowering 9.08±0.29a 2.06±0.08b 1.83±0.19bc 1.62±0.26c Fruiting 9.11±0.11a 2.06±0.16b 1.71±0.24bc 1.59±0.24c Note: On the same row, the different characters (a-b-c) gave the significant difference (5%, Duncan). The average of TKN of wastewater from catfish pond had reduced by rice growth stage while going through rice. The results shown that, rice is more growth, TKN absorption ability is higher. While no chemical fertilizer supplement, the nutrient of waste water had been used by rice leading to outlet TKN was lowest at the treatment of K supplement only. 4.3.2.7 The concentration of NH4+ (mg/L) of waste water after treated by paddy field NH4+ had trended to reduce at all treatment after going through paddy field significantly. Simultaneously, this reduction had made the statistic meaning diffirence (5%) between before and after irrigating. NH4+ of seeding was higher than NH4+ standard of NTR 08:2015/BTNMT column B1. However, NH4+ of flowering and fruiting was met NH4+ standard of NTR 08:2015/BTNMT column B1. Table 4.7 NH4+ of catfish pond waste water before and after going through paddy field NTR NH4+ (mg/L) 08:2015/ Wastewater BTNMT Stage NPK 2/3 NPK K of catfish (B1 supplement supplement supplement pond column) treatment treatment treatment treatment Seeding 1.21±0.16a 0.90±0.11b 0.84±0.09b 0.73±0.10b Tillering 1.77±0.16a 0.93±0.16b 0.56±0.00c 0.37±0.16c Booting 2.52±0.00a 1.31±0.16b 0.65±0.16c 0.37±0.16d 0,5 Flowering 2.52±0.16a 0.52±0.05b 0.34±0.12bc 0.16±0.08c Fruiting 2.67±0.18a 0.33±0.05b 0.33±0.00b 0.20±0.02b Note: On the same row, the different characters (a-b-c) gave the significant difference (5%, Duncan). 14
The same of TKN concentration, outlet NH4+ is lowest at fruiting stage at all of treatment. Athought in this stage, NH4+ is higher than other stages. Thus, rice is more growth, the nutrient absorbtion ability in waste water is higher. 4.3.2.8 The concentration of NO3- (mg/L) of wastewater after treated by paddy field NO3- had clearly reduced all of paddy growth stage at all of treatment after going through paddy field (Table 4.8). NO3- of wastewater from catfish pond before and after treated was entirely met NO3- standard of NTR 08:2015/BTNMT column B1. Table 4.8 NO3- concentration of catfish pond waste water after going through paddy field NTR NO3- (mg/L) 08:2015/B Wastewater TNMT Stage NPK 2/3 NPK K of catfish (B1 supplement supplement supplemen pond column) treatment treatment t treatment treatment Seeding 0.42±0.04a 0.28±0.03b 0.26±0.02b 0.28±0.03b Tillering 0.44±0.01a 0.14±0.01b 0.12±0.01bc 0.11±0.01c Booting 0.41±0.02a 0.14±0.02b 0.11±0.02bc 0.09±0.02c 10 a b b b Flowering 0.46±0.03 0.15±0.04 0.14±0.03 0.11±0.02 a b bc Fruiting 0.45±0.01 0.29±0.02 0.27±0.00 0.26±0.01c Note: On the same row, the different characters (a-b-c) gave the significant difference (5%, Duncan). 4.3.2.9 TP concentration (mg/L) of waste water after treated by paddy field After going through paddy field of waste water from catfish pond treatment and different provided chemical fertilizer treatments, TP of water column is statistic meaning difference (5%). Table 4.9 TP concentration after going through paddy field TP (mg/L) Waste water Stage NPK 2/3 NPK of catfish K supplement supplement supplement pond treatment treatment treatment treatment Seeding 0.84±0.02a 0.24±0.01b 0.25±0.02b 0.24±0.03b Tillering 0.92±0.02a 0.24±0.03b 0.19±0.04bc 0.15±0.03c Booting 0.94±0.01a 0.28±0.03b 0.18±0.04c 0.15±0.03c Flowering 0.94±0.03a 0.16±0.00b 0.15±0.02b 0.14±0.01b Fruiting 0.90±0.01a 0.05±0.02b 0.04±0.01c 0.02±0.01c Note: On the same row, the different characters (a-b-c) gave the significant difference (5%, Duncan). 15
At all of waste water irrigation treatments, the treatment of K supplement only had TP removal higher than others. TP concentration had a trend to reduce according to paddy growth stage while irrigating. 4.3.4 Rice productivity With the highest nutrient supplement by irrigating wastewater and NKP supplement treatments, filled grain is lowest (87%), while filled grain is highest at the treatment of K supplement only (91.7%) (Figure 4.9). Filled grain rate is decided by the number of panicle as well as branches per panicle (Nguyen Ngoc De, 2008), and is affected on paddy rice yield due to less filled grain while higher unfilled grain per panicle is reduced yields (Dinh Van Lu, 1978 cited in Nguyen Thi Be Phuc, 2008). TỷRate lệ hạtof chắc/bông (%) filled grains/spikelet (%) 1000-grains weight (gram) 93 91.7 30.0 23.5 24.2 25.2 92 23.9 91 25.0 90 20.0 89 88.0 87.6 15.0 88 87.0 87 10.0 86 85 5.0 84 0.0 1 2 3 4 Nghiệm thức Treatment Treatment 1 2 3 4 Figure 4.1 Characteristics of rice grains Figure 4.2 The weight of 1000 grains (g) Rice yield (tons/ha) 10 7.2 7.7 7.5 8 6.6 6 4 2 0 1 2 3 4 Treatment Figure 4.3 Rice yields from all treatment Note: Treatment 1:river water + NPK; Treatment 2: waste water + NPK; Treatment 3: waste wtare + 2/3 NPK; Treatment 4: waste water + K At the treatment of wastewater, the grain weight is heavier than the less chemical fertilizer treatment and vice versa (Figure 4.2). The treatment of K supplemt only, the grain weight is highest (25,2 g/1.000 grains), while the treatment of the most NPK supplement is the lowest grain weight (17,8 g/1.000 grains). Figure 4.3 shown that, the highest yield (7,7 tons/ha) is the treatment of waste water and NPK, and the lowest is the treatment of K supplement only (6,6 tons/ha). Besides, with the treatment of waste water and 2/3 NPK supplement, the rice yield is higher than the traditional cultivation. 16
4.3.4.3 Cost and benefit Through calculated results shown that, case 3 had the benefit 20 million/ha higher than others. Case 1 had the lowest benefit 16.5 million/ha. It is confirmed that wastewater of catfish pond was able to contribute a large amount of organic fertilizer for paddy field, leading to save cots for rice cultivation and increase the benefit for farmers. 50 38.5 37.5 40 36.0 (Million dong/ha) 33.0 30 Thành tiền 19.5 20.0 18.5 Revenue 19.5 19.0 20 16.5 17.5 14.5 Cost Chi phí Benefit Lợi nhuận 10 0 Nghiệm thức 11 Nghiệm Treatment thức 22 Nghiệm Treatment thức33 Nghiệm Treatment thức44 Treatment Figure 4.4 Revenue, cost and benefit after harvesting Note: Treatment 1:river water + NPK; Treatment 2: waste water + NPK; Treatment 3: waste wtare + 2/3 NPK; Treatment 4: waste water + K 4.3.5 Nitrogen, phosphorus concentration in the wastewater after going through paddy field and nitrogen, phosphorus, potassium accumulation in the paddy stem and grain in the Winter - Spring crop 2013 - 2014 4.3.5.1 Nitrogen, phosphorus concentration in the wastewater after going through paddy field Table 4.10 Nitrogen and phosphorus concentration in the waste water is absorbed after going through paddy field at each treatment NH4+ NO3- TKN TP Stage Treatment (mg/L) (mg/L) (mg/L) (mg/L) NT1 0.99±0.04c 0.01±0.00c 5.02±0.93 0.55±0.06d NT2 1.15±0.09b 0.02±0.00bc 5.60±0.53 0.79±0.06c Seeding NT3 1.57±0.08 a 0.03±0.00 a 6.18±0.40 1.14±0.13a NT4 1.26±0.06b 0.03±0.00ab 5.95±0.53 0.95±0.05b a c NT1 1.36±0.15 0.04±0.00 7.15±0.35c 1.73±0.03d NT2 1.53±0.05bc 0.05±0.00b 7.55±0.22c 2.03±0.05c Flowering NT3 2.29±0.34a 0.06±0.00a 9.08±0.34a 2.59±0.07a NT4 1.82±0.12b 0.05±0.01b 8.27±0.08b 2.34±0.04b NT1 3.34±0.05d 0.04±0.01c 11.07±0.18d 3.69±0.06d NT2 3.99±0.12c 0.07±0.02b 13.20±0.11c 4.29±0.06c Fruiting NT3 5.62±0.13b 0.12±0.01a 15.16±0.05a 4.91±0.11a NT4 4.61±0.09a 0.06±0.01b 13.80±0.40b 4.48±0.12b Note: On the same column, 1 stage, the different characters (a-b-c) gave the significant difference (5%, Duncan). NT1: Irrigating wastewater on the soil, NT2: Rice irrigated by wastewater without NPK, NT3: irrigated by wastewater and 2/3 NPK, NT4: irrigated by waste water and NPK. 17
At each of cases, nitrogen and phosphorus concentration are the highest reduced as NT3 and the lowest as NT 1 (Table 4.10). At NT1, nitrogen and phosphorus absorption ability was in range of 5.02 mg/L±0.93 to 11.07 mg/L±0.18 (TKN) and 0.55 mg/L±0.06 to 3.69 mg/L±0.06 (TP). The cause can be that rice stem of this treatment is no more absorbed the nitrogen and phosphorus than others. At NT3, nitrogen and phosphorus absorption ability was the highest and in range of 6.18 mg/L±0.40 to 15.16 mg/L±0.05 for TKN and 1.14 mg/L±0.13 to 4.91 mg/L±0.11 for TP. Due to less chemical fertilizer, leading to no abundant of nitrogen and phosphorus on environment, the rice will use the nutrient from waste water to grow and develop effectively. 4.3.5.2 Accumulation of nitrogen, phosphorus and potassium in the rice stem (% dry biomass) Nitrogen, phosphorus and potassium concentration in the rice stem by time is shown on table 4.11. Statistic data cited that, there is no meaning difference between each of treatment at each growth stage of rice. Table 4.11 Total nitrogen, phosphorus and potassium at rice stem (%) Stage Treatment TN (%) TP (%P2O5) TK (%K2O) NT 2 2.46±0.32 0.99±0.11 1.91±0.09 Seeding NT 3 2.52±0.47 1.01±0.15 2.03±0.02 NT 4 2.60±0.50 1.07±0.03 2.18±0.05 NT 2 1.31±0.11 0.61±0.03 1.95±0.16 Flowering NT 3 1.36±0.05 0.68±0.05 1.97±0.03 NT 4 1.39±0.08 0.70±0.05 2.00±0.07 NT 2 0.93±0.09 0.54±0.06 1.22±0.26 Fruiting NT 3 0.95±0.12 0.64±0.06 1.54±0.06 NT 4 1.01±0.03 0.67±0.07 1.72±0.07 Note: NT2: Paddy irrigated by waste water without NPK fertilizer, NT3: irrigated by waste water and 2/3 NPK fertilizer, NT4: irrigated by waste water and NPK fertilizer. Phosphorus accumulation in rice stem was the lowest at seeding stage and the highest at fruiting stage (Table 4.11). Phosphorus concentration (%P2O5) in rice stem was the lowest at fruiting stage and the highest at seeding stage. At NPK supplement treatment, TP in rice stem is in range of 0.64%0.06 to 1.01%0.15, meant that reduced 0.37%. When flowing rice, around 37-83% of phosphorus concentration had been moved to grain (Nguyen Ngoc De, 2008). Potassium concentration (%K2O) in rice stem was around 2.18% at the seeding stage and around 1.72% at fruiting stage of NPK supplement treatment, meant that reduced 0.46%. At 2/3 NPK supplement treatment, potassium concentration in rice stem was around 2.03% at seeding stage and 18