Technical Report (CARD 023/06 VIE) Improvement of water quality of outflows from ponds to waterways Cao van Phung 1 and Bell R.W. 2 1. Cuu Long Rice Research Institute, O’Mon, Cantho Province, Vietnam. Email: caovanphung@hcm.vnn.vn 2. School of Environmental Science, Murdoch University, Murdoch 6150, Australia. Summary In the Mekong Delta of Vietnam, water quality is critically important for human health and wellbeing as well as ecosystem function. Catfish farming in the Mekong Delta, which is mostly confined to the provinces of An Giang, Cantho, Dop Lap and Vinh Long, is considered to be a significant source of water pollution in those provinces. A survey of 240 catfish farmers in An Giang and Cantho provinces, and of Clarias fish farmers in Cantho Province confirmed that discharge of waste water and solid waste from these operations is directly to public water sources in canals and rivers in over 75 % of cases. Water consumers in the areas where catfish ponds are prevalent had a strong perception that catfish pond discharge was the major cause of degraded water quality. Water sampling at 2 points of discharge in An Giang over a 5-month period confirmed that discharge causes canal water to exceed discharge standards for COD, TSS and NH 4 . However, even background levels were generally above the levels set for household use in Vietnam. Two case studies showed that passing Clarias fishpond waste water or water laden with catfish waste through rice fields improved its quality substantially, by decreasing TSS, COD, BOD, N and P. Coupled with evidence that catfish and Clarias fish pond wastes can be an effective partial replacement of rice fertiliser requirements, these results indicate that recycling solid waste and waste water from fishponds could be promoted as an effective technology for improving quality of public water ways. The recent decline in density of active catfish ponds in the Mekong Delta, during to poor profitability, may be having a beneficial effect on water quality.  1 Corresponding author Cuu Long Rice Research Institute, O’Mon district, Cantho city-Vietnam. Phone No (84) 710861452. Fax: (84) 710861457. Email: caovanphung@hcm.vnn.vn Contents  Introduction  Baseline study  Water quality in canals receiving discharge from fish ponds  VAC water quality study  Water quality after passage through padi fields  Fishpond waste loading in rice padi fields  A strategic framework for determining application rates for fishpond waste Introduction The main aim of the present project was to develop effective methods for decreasing pollution of water from catfish pond waste discharge. In other reports, the treatment of solid waste and waste water has been examined (Cao et al. 2010a,b). In the present report, the emphasis is on quality of water in fishponds and in water affected by the discharge. The report considers water quality issues associated with catfish as well as for Clarias fish raised in the VAC system. In this report, the results of a baseline study were used to demonstrate forms of water pollution caused by discharge from catfish ponds, from the perspective of farmers, and also by field sampling at two locations. Water quality sampling was then used to determine the effectiveness of wastewater treatment by recycling it through rice padi fields. Finally, there is a discussion of the principles that are expected to govern future use of waste water treatment through discharge to rice padi fields. Baseline study in Cantho and An Giang A survey was conducted in October-November 2007 in Cantho city and January- February, 2008 in An Giang province. In total 240 questionnaires completed by stakeholders (rice and fish farmers were sampled in equal numbers) were collected (2 districts/province) (Table 1, 2). The baseline survey was reported fully in April 2009 (Cao et al. 2009). Key findings of the study are discussed below to highlight the main water quality concerns, as perceived by the farmers. In addition, the survey reported on the prevalence of fish and human diseases, which may be indicators of water quality. Water quality Generally half or less of the farmers were satisfied with water quality, and 15-24 % classified it as bad. Yet, only 5-8 % of fish farmers had their own settling pond and the vast majority discharged waste to canals and rivers directly without treatment. Phan et al. (2009) in a survey of 89 catfish farms along the main rivers of the Mekong Delta found only 3 % of farmers reported having settling ponds. However, 15-24 % of catfish farmers in the present study used rice padi fields for discharge of waste water. Waste from fishpond was perceived to be the major source causing pollution in An Giang while in Can Tho 37 % of respondents considered catfish ponds the major cause for poor water quality. Part of the reason for the different responses may be that 50 percent of respondents in An Giang used river water for household purposes while a similar proportion of people in Cantho utilized tubewell water (Cao et al. 2009). Farmers were also concerned of threats to fish culture from pesticides discharges from paddy fields. The type of feed and additives supplied to catfish may have a bearing on water quality. In Cantho province the majority of catfish farmers supplied pellets to the fish, while in An Giang, most farmers prepared their own feed (Table 3). Both supplemented the feed with vitamins, enzymes and minerals. According to De Silva et al. (2010) farm-made feed increases P discharge but not N discharge relative to pelleted feed. Table 1. Farmers’ perception of water quality in surface water close to their residence, and current waste discharge practices for catfish farmers. Values are percentages for respondents, where N=60 for each of the 4 groups of respondents. Items Cantho An Giang Fish culture Rice culture Fish culture Rice culture Water quality (%) - Good - Medium - Bad 30 52 18 55 22 23 51 25 24 46 39 15 Wastewater discharge - River or canal - Paddy - Settling pond 80 15 5 100 68 24 8 100 Table 2: Reasons given for poor quality of water for irrigation and for household use by catfish and rice farmers. Values are a percentage of respondents where N= 120 in each province. Items An Giang (%) Can Tho (%) Waste from fishpond 91 37 Pesticides from paddy 9 15 Others 0 48 For water treatment in catfish culture, nearly 50 % of farmers at both sites had used Vikong, BKC, Bioca, Yulai, Aquapure, Prawbac and some others (Table 4). They also used antibiotics to control mainly bacterial diseases in the digestive tract of catfish. Some common antibiotics like Amoxycilline, Cotrim, Penicilline, Kanamycine, Oxamet, Tetracylline.were used by mixing into feeds in An Giang (96 %) or putting directly into water by 40% of farmers in Cantho. Almost all of farmer reported using antibotics at recommended dosage. For control of algae in fishponds, 93 % of farmers in Cantho and about 66 % in An Giang province applied copper sulphate, BKC, Vikong, Chlorine, juka and even salt or lime (Table 4). It is worth noting that fishpond solid waste generally contain significant but not excessive levels of Cu (Table 14). Amongst the treatment chemicals used, BKC and chlorine were the most common both in An Giang and Cantho. Table 3: Characteristics of feed and additives used in catfish farms. Values are a percentage of respondents where N= 60 in each province. Items Can Tho An Giang Type of feed (%) Pellet (from industry) 55 27 Ball (farm-made produce) 37 58 Mixed (pellet+ ball) 8 15 Use of additive 88 66 Types of additive Vitamins 64 69 Enzyme 57 74 Minerals 23 36 Table 4: Chemicals used for water treatment in catfish farms. Values are a percentage of respondents where N= 60 in each province. Items Cantho An Giang Bio-products (%) 48 43 Antibiotics (%) 72 54 Mixing to feed 60 96 Mixing with fishpond water 40 4 Water treatment 97 100 BKC 21 28 Vikong 43 5 Copper sulfate 7 8 Chlorine 21 10 Others 8 49  All farmers normally spread lime or salt along the sides and bottom of ponds after making new ponds or after draining out the water from harvested ponds. Dosages of lime and salt varied from 300-400 kg/ ha. Pond are kept dried for 3-5 days before re- filling with water for a new crop of fish. More than 95 % of farmers changed and/or added water to fish ponds regularly (about 1/3 volume of pond daily) and there was about 50 % farmers at both sites practiced bottom of fishpond cleaning by pumping out sludge during the growth of catfish. In addition, all of the farmers pumped sludge out of their pond after harvesting fish (Table 5). The practice of discharge of solid waste directly to water sources was practiced by 63-70 % of catfish farmers (Table 6). Most farmers had a handheld pH meter to monitor water quality (Table 5). Other ways to detect water quality were by observation of water colour or smelling the odour of water. Farmers conclude that oxygen is deficient if most of fishes come to the pond surface during the early morning. Table 5: Water management in catfish culture. Values are a percentage of respondents where N= 60 in each province. Items Cantho An Giang Renewed fishpond water (%) 100 100 Lime (kg/ha) 425 350 Salt (kg/ha) 325 300 Dried bottom of pond (%) 100 100 Days of drying 3.5 4 Filled up and/or changed water periodically (%) 98 100 Volume of added or changed water 1/3 1/3 Water quality monitoring pH 95 90 Color or odour 8 12 NH 3 and Oxygen 62 65 Farmers raising catfish usually clean organic wastes in fishpond to prevent disease spread to fish (Table 6). Survey data indicated that most of sludge was discharged directly to water source (63 %), other uses of sludges including filling up low elevation areas or mulching of fruit trees (37 %). Sludge removal occured 1 or 2 times (97 %), but more than 2 times was uncommon. Sludge removal was by using bottom pond pump (86%) or draining out all water in fishpond then removing sludge by hand (14 %) Fish disease As shown above, most of the surveyed farmers in Cantho and An Giang discharged waste directly into canals and rivers. The discharge of waste from fishponds may be a significant vector for the spread of infection to neighbouring ponds. In the baseline survey, there was a high prevalence of fish diseases reported by farmers in both Cantho and An Giang provinces (Table 7). Over 65-73 % of fishpond farmers experienced symptoms of haemorhage or swelling head in their fish, especially at fingerling stage. In Chau Phu, Phu Tan, Thot Nhot and Cantho districts there is a concentration of fishponds within a relatively small area, usually in locations with good access to river or main canal water. All fishponds along a section of the canal or river are obtaining water for catfish ponds from a common source. Hence disease organisms may spread readily from one operator to another. The dispersion of disease-causing organisms in the canals and river has not been investigated in the present study, although the dispersion plume for TSS in waste water was at least 600 m from the point of discharge. While the farmers reported that effective control measures for major diseases were generally available, reducing the spread of the disease through better water quality may be an outcome from more effective treatment of wastes from fish ponds. Table 6: Solid waste management on catfish farms. Values are a percentage of respondents where N= 60 in each province. Items Cantho An Giang Removing sludge purpose Sanitation 51 65 Disease control 46 35 Methods of discharge Pumping sludge 86 89 Removing by hand 14 11 Location of sludge discharge Water course 70 63 Filling up low lying surface 30 Mulching of fruit trees 37 Times of sludge discharge One time 37 35 Two times 60 59 Three times 3 6 Sludge discharge schedule During raising time (%) 50 50 After harvesting 60 75 Reports on human diseases caused by water pollution: Investigations on human diseases attributable to water pollution were completed in OMon and Thot Not districts of Cantho City and in Chau Phu and Phu Tan districts of An Giang province. According to data collected at the Preventive Medicine Center in O Mon and Thot Not districts, during 2006 and 2007, prevalence of dengue increased. This disease re-occurred at the end of 2008 mainly in the south of Vietnam; the situation was most severe in An Giang and Dong Thap provinces (Department of Preventive Medicine – MOH Vietnam, 2008). Data in Table 8 also indicated that diahorrea in 2007 was higher than in 2006. Dengue, diahorrea and dysentery in Phu Tan were much higher than those in Chau Phu and they had a tendency to increase (Table 9). These might be related to the closed dike system at Phu Tan district where water in canals could not be drained. As reported in the Baseline survey, most of people in An Giang province (57 %) are still using river or canal waters as the main source for household use. Table 7: Diseases of catfish, occurrence stage and control measure. Values are a percentage of respondents where N= 60 in each province. Items Cantho An Giang Symptoms Haemorhage 55 67 Swelling head 10 6 Slimy loss 0.1 4 Occurrence stage Fingerling up to 1 month 72 88 From 1-3 month old 17 8 More than 3 month old 11 4 Effective Control Haemorrhage 92 82 Swelling head 77 Slimy loss 100 While not a rigorously collected set of data, the information on human disease trends in two districts with a high concentration of catfish ponds may be related to the rapid spread of fishponds in recent years. Table 8: Disease reports to Preventative Medical Centre in 2006 & 2007 at O Mon and Thot Not districts Disease O Mon Thot Not 2006 2007 2006 2007 Dengue 179 237 246 546 Typhoid fever 2 0 Diarrhea 159 220 3210 2822 Dysentery 0 1 138 31 Table 9: Disease reports to Preventative Medical Centre in 2006 & 2007 at Phu Tan and Chau Phu districts Disease Phu Tan Chau Phu 2005 2006 2007 2005 2006 2007 Dengue 112 300 495 411 595 438 Typhoid fever 169 153 71 Diarrhea 752 957 1502 189 187 200 Dysentery 202 250 463 21 10 Water quality in canals receiving discharge from fish ponds Three study areas were selected for water quality sampling: Chau Phu and Phu Tan in An Giang Province; Thot Not in Cantho district. Study areas have a high concentration of catfish ponds (Phan et al. 2009). Water quality sampling was also conducted in Binh Thuy and Phong Dien districts near Cantho city, in areas practicing VAC. Water samples at Chau Phu and Phu Tan during the dry and wet season (especially at flooding time) were collected at the flush gate, 100 metres up-stream and 100, 200, 300, 400 and 500 metres down-stream. These were measured for pH, EC, TSS, COD and NH 4 -N. Samples of water in the canal were collected at 15-day intervals for 5 months both before discharge and 1-2 hours after discharge had occurred (December to April). Data in Figure 1 shows that pH of waters before opening the flushing gate was higher than after discharge; however, the values were not significantly different (P < 0.05) in both dry and wet seasons. During flooding time, the difference between these two sets of data were even smaller than those taken in the dry season because the dilution factor during the flooding time was much greater (data not shown). Generally pH in the canal after waste water discharge was within limits accepted for living use (TCVN-5492-2005). Electrical conductivity taken after opening the canal gate to release fishpond waste water were statistically higher than values measured before (Fig. 2). However, as with pH, EC values during flooding time were not significantly different between times of water sampling. Unlike pH but similar to EC, average COD values were very significantly different before and after opening the flushing gate (Fig. 3). The increase in COD persisted even during flooding time. On average, the COD levels declined with distance from the point of discharge. At 500 m from the discharge, they had almost halved but were still well above the pre-release values. Figure 1: pH of water in canal before and after opening the flushing gate to discharge fishpond waste water. Values are means of 40 values sampled at 15-day intervals for 5 months (December to April) in two sites of An Giang Province (Phu Tan and Chau districts). Figure 2: Electrical conductivity (EC) of water in canal before and after opening the flushing gate to discharge fishpond waste water. Values are means of 40 values sampled at 15-day intervals for 5 months (December to April) in two sites of An Giang Province (Phu Tan and Chau districts). Normally COD of liquid waste from fish ponds exceeded values allowable for living use (below 10 mg/L) except during the flooding time (October-January). Indeed, even the values in the main canal before discharge of waste water were generally > 10 mg /L. All values, before and after discharge were in the range accepted for water discharge from fish ponds (35 mg/L <COD<100 mg/L). 0 50 100 150 200 250 300 350 -100 0 100 200 300 400 500 m Ec (uS/cm) Before After 6.9 7 7.1 7.2 7.3 7.4 7.5 -100 0 100 200 300 400 500 m pH Before After [...]... wastewater on canal water quality for at least 100 m up-stream and 500 m downstream of the discharge The measurable decline in water quality was attributed to elevated COD, NH4 and TSS These water quality data support the results of the baseline survey of farmers In Cantho and An Giang, 7-36 % of farmers assessed water quality to be bad, and of these 37 to 91 % attributed the poor water quality to catfish... to rice padi fields, settling ponds and small wetlands to discharge into another main canal (Fig 6) Water samples were analysed for ammonium-N, nitrate-N, total N, TSS, COD and total P (Table 14) During the passage of the water in Chau Phu from the fishpond-polluted main canal to the discharge canal, levels of N and P dropped 3- to 4-fold (Table 14) The water COD also dropped from over 230 mg /L to. .. widespread use of this practice to treat waste and improve the quality of water in canals and rivers, a number of factors need to be considered The loading of waste to land depends on optimising four criteria: hydraulic loading; solids loading; chemical reactivity of the waste, and; nutrient assimilation capacity of the system The optimisation of these factors in relation to fishpond waste application to rice... waste water discharge The concentration of nutrients and levels of COD and BOD are much higher in solid waste than wastewater, but the large volume of wastewater means that total nutrient loading may be as high With very frequenct water replacement, the composition of waste water may not be too different from that of canal water (Bosma et al 2009) In the survey of Cantho and An Giang, fishpond operators... be needed to deal with waste water In the wet season, larger areas of rice fields are needed to cater for the water from a single pond The timing of rainfall also has a bearing on the timing of wastewater application to padi fields Antecedent rainfall may block the use of wastewater in a particular field for several days Hence, it is important for the flexibility of operations of fishponds to arrange... longevity of these peaks in water quality to ascertain whether they persist for minutes, hours or days The persistence of the peaks in water pollution due to fishpond discharge are likely to relate to the level of pollution in the discharge water, and the volume of discharge in relation to water flow in the canal Small canals in the dry season with limited flow for flushing are most likely to suffer... receiving discharge from a large number of catfish ponds It was then directed through rice fields to another main canal Water samples were collected along this water course In the second case, water was sampled from a Clarias fishpond and then at a series of downstream locations to determine changes in composition and quality In Chau Phu, water samples were collected along the course of water from a main drain... wastewater Assuming a fish harvest of 300 t/ha/yr from fishponds, and a feed conversion of 1 tonne of fish biomass for every 1.86 t of feed, 1 ha of fishpond generates about 260 t of organic waste Assuming an application rate of 3 t/ha, this requires about 90 ha of padi land per 1 ha of fishpond This represents a minimum ratio since greater than 90 ha would be advisable to minimise the risks of nutrient... capacity of padi fields or settling ponds on which to apply wastewater, to avoid the situation of having no storage available for wastewater disposal when discharge is required from the fishpond From a case study at Chau Phu, An Giang Province, it was reported that growing 3 rice crops per year required 12-13 irrigations, each supplying about 75 mm of water Hence in this location, 900-1000 mm of irrigation... in water quality Water quality in catfish ponds: Investigations were conducted from December 2007 to July 2008 at Phu Tan and Chau Phu districts of An Giang province on water quality in 12 catfish ponds that used two types of feed, namely manufactured pellets and farm-made feed Results showed that pH values were still within the acceptance limit (7.0-8.0) even though there were differences between ponds . Technical Report (CARD 023/06 VIE) Improvement of water quality of outflows from ponds to waterways Cao van Phung 1 and Bell R.W. 2 1. Cuu Long Rice Research. may be indicators of water quality. Water quality Generally half or less of the farmers were satisfied with water quality, and 15-24 % classified it as bad. Yet, only 5-8 % of fish farmers. TSS. These water quality data support the results of the baseline survey of farmers. In Cantho and An Giang, 7-36 % of farmers assessed water quality to be bad, and of these 37 to 91 % attributed