An Integrated Pollution Prevention Ecosystem for Small-Scale Production of Raw Coco-nut Jelly in Craft Villages——A Case Study from Mekong Delta,Vietnam

Le Thanh Hai,Tra Van Tung,Tran Van Thanh,Le Quoc Vi,Nguyen Thi Phuong Thao,Tran Thi Hieu,Son Le,Sibylle Braunegg,Gerhart Braunegg,Hans Schnitzer†

1 Institute for Environment and Resources,National University of Ho Chi Minh City,Ho Chi Minh 740500,Vietnam

2 Water and Environmental Engineering,Nagasaki University,Nagasaki 852-8521,Japan

3 Institute for Process and Particle Engineering,Graz University of Technology,Graz A-8010,Austria

4 ARENA Research for Sustainable Resources,Graz A-8010,Austria

Keywords Bacterial cellulose Ecosystem Cleaner production Integrated pollution reduction Nata de coco

Abstract Raw coconut jelly is a popular byproduct of the coconut processing industry in the Asia Pacific which can enhance the added economic value for the local families in the rural area. However,the coconut jelly production has resulted in significant environmental impacts,particularly to the aquatic environment due to its heavily polluted wastewater e.g. very high values of COD(up to 120,000 mg/l),of total nitrogen(up to 1,740 mg/l),and of total phosphorus(up to 64 mg/l).The available wastewater treatment technology for such type of wastewater is likely to be not economically efficient due to the small-scale production at craft villages in the developing countries.This study developed and demonstrated an integrated eco-model for small(family) scale production of raw coconut jelly in craft villages which applied Cleaner Production sollutions for pollution prevention on the basis of available conditions at the local family. The system demonstration showed a win-win solution for family with major benefits by reduction of 90%of pollutants(i.e 27 kg COD, 21.4 kg BOD5, approx. 7 kg N, 113 g P and 28 kg Sfor one production batch),as well as the other benefit by major reduction of 90%of investment and operating costs of the wastewater treatment plant.

1 Introduction

1.1 Bacterial cellulose production

Cellulose production by microorganisms(known as Bacterial CelluloseBC)and its applications have been wellreviewed by Jozala et al. (2016)BC has been firstly discovered by Schramm and Hestrin in 1954(Jozala et al.,2016). The first medium to produce BC in 1954 was called Hestrin and Schramm(HS)consisting of 2%glucose,0.5%peptone,0.5%yeast extract,0.27%of anhydrous disodium phosphate,and 0.15%citric acid monohydrate(Jozala et al., 2016). This medium was not economically efficient for large-scale production therefore various media were studied for growing BC microorganisms,for instance,HS combined with 1%lignosulfonate(Keshk and Sameshima, 2006), sucrose (Mikkelsen et al., 2009), orange juice combined with nitrogen source of HS(Kurosumi et al., 2008), glucose with MCP-1 (Hu and Catchmark, 2010), molasses combined corn juice and acetic acid (Jung et al., 2010), glucose (Carreira et al., 2011), HS with n-butanol (Lu et al., 2011), HS with thin stillage.()(Wu and Liu,2012),residues from olive oil production(Gomes et al.,2013),molasses.().(Cakar et al., 2014), waste beer yeast treated with ultrasonication .()(Lin et al., 2014), rotten fruit culture (Jozala et al., 2015), wood hot water extract (Kiziltas et al., 2015), candy production wastewater (Zheng Li et al.,2014),orange, lemon juice and sugar(Kim et al.,2015), wastewater from lipid fermentation (Huang et al.,2016) and from coconut water(Budhiono et al.,1999)

Cellulose produced by microorganisms is of a very high quality due to its small size,purity and no content of hemicellulose and lignin(Carreira et al.,2011;Esa et al.,2014). Bacterial Cellulose and Bacterial Cellulose composite are therefore widely used for food industry,health protection mask(Rahmayanti et al.,2018),medical materials and electrical equipment(Esa et al.,2014).

1.2 Production of bacterial cellulose with coconut water(coconut jelly)

Coconut is an important agricultural tree in the tropical countries of the Asia Pacific, mainly in India and in Southeast Asia. Indonesia, Philippines,Thailand,Malaysia and Vietnam are the most coconut-rich countries in Southeast Asia(Punchihewa and Arancon,1999). By 2018,Vietnam’s coconut production was ranked 6th in the world,with an output of 1,303,826 tons which covers only about 2.1%of the world coconut production(Burton,2018), while 3 largest coconut production countries are Indonesia, the Philippines and India which cover 31.5,26.3 and 20.4%of world coconut production respectively(Naik,2017).

Coconut can be used to produce many different products such as dried coconut meat,coconut candy,coconut oil,activated carbon,coconut fiber,coconut handicrafts, fresh coconut water,and jelly coconut. In addition,coconut products are also applied to many different purposes such as producing MDF-Medium Density Fiberboard,HDF-High Density Fiberboard(Freire et al.,2017)and many other products such as sugar,alcohol,soap,etc.

Coconut water is a byproduct of the coconut meat production processes. Coconut water discharged from this process has been utilized to produce food additives and coconut jelly. The BC product from coconut water is known as coconut jelly and is used as a long-term food in Southeast Asia since the 1980s (Budhiono et al.,1999). In addition,coconut jelly can also be produced by extracting coconut milk from coconut(Punchihewa and Arancon, 1999). In Vietnam,Ben Tre province is the province with the largest area of coconut cultivation and the concentration of coconut processing industry,Ben Tre alone disposes of a total production capacity of crude coconut jelly of about 15,000 tons/year(Phisalaphong et al.,2016). Most coconut jelly production facilities are household(family)scale and distributed in rural areas to take advantage of idle labor,offering additional income especially to women.

1.3 Environmental impacts

The coconut juice shows a high content in C,N,and P,and the majority of C content can be transferred to the final product(jelly),but the N and P contents will subsequently remain in the wastewater during the production.There are a few studies reporting the characteristics of such wastewater e.g. VNCPC(2011) and Tran(2012).In Vietnam,the production of raw coconut jelly results in large amounts of wastewater mainly from the process of soaking, pressing jelly, washing trays, sterilizing and cleaning of the equipments. The water consumption norm is about 5-6 m3/ton of product, consumption of ammonium sulphate (AS)is about 7.2 kg/ton of product,acetic acid is about 2.5 g/ton of product,and sugar is about 10.8 kg/ton of product(VNCPC,2011). Wastewater from raw coconut jelly production has high organic, N,and P contents, which lead to high Biological Oxygen Demand(BOD),then it could affect the water environment(when BOD levels are high,dissolved oxygen(DO)levels decrease because the oxygen that is available in the water is being consumed by the bacteria, and since less DO is available in the water,fish and other aquatic organisms may not survive...). A typical analysis result shows that COD is about 23,400mg/l,BOD5:16,200 mg/l,total nitrogen: 1,740 mg/l,total phosphorus: 64 mg/l(VNCPC,2011). Another study has found that COD value in wastewater from the production of coconut jelly varies from 37,500 to 120,000 mg/l (Amongo, 1995). The largest amount of wastewater generated during the production of coconut jelly is from the process of washing the trays,and the wastewater from this process has a large quantity but the pollutant load is much lower than that in the wastewater from the process of soaking and pressing the jelly.

Another significant quantity of wastewater generated from the processing raw coconut jelly is from the processes of soaking and crushing of the jelly. Wastewater generated from these stages have high levels of polluted organic compounds, in addition, the wastewater is also heavily polluted by nitrogen, phosphorus, and(1,437-2,997 mg/l)due to the use of fertilizers. Ammonium sulfate(AS)and NPP(Nitrogen-Phosphorus-Potassium) fertilizers are used for soaking the jelly in the production process, and the results from wastewater analysis done by Tran(2012)showed that almost the whole sulfate content in AS and NPP materials have gone into the wastewater.

In order to treat wastewater with high concentrations of organic compounds, nitrogen and phosphorus, biological methods are usually applied, and the treatment facilities consist of an anaerobic digester and an aerobic treatment tank. The anaerobic and aerobic wastewater treatment processes are often combined with purpose to maximize the final treatment efficiency. However, for wastewater from coconut jelly production, it is not possible to apply under simple treatment method following the aerobic and anaerobic mechanism due to the presence of high sulfate content in the wastewater. The high content of sulfate in coconut milk wastewater will affect both the anaerobic and aerobic treatment processes, thus reducing the treatment efficiency (Cervantes et al., 2006). Therefore, it is necessary to have a preliminary sulfate treatment facility before proceeding to aerobic and anaerobic treatment facilities. To overcome this disadvantage, and in order to adjust the COD:sulfate ratio higher than 10 for the ease(optimum performance)of the anaerobic treatment process in the next step,the author Tran(2012) has performed an experiment to reduce sulfate content by using a sulfate reduction tank in the system. This author has proposed a method of reducing SO2-4 content in wastewater flow with a capacity of 5-10 m3/day,but the initial construction investment cost is quite high,about 135,162 to 173,842 VND(Vietnam Dongs, e.g., 5.8-7.45 USD)for 1 m3of wastewater, and the operating cost is also high (19,035-48,283 VND,e.g., 0.81-2.07 USD) for 1 m3of wastewater (Tran, 2012). If adding organic and N treatment facilities to the system,the cost is even higher and it is completely unsuitable for raw coconut jelly producers at small scale in developing countries. This is a great barrier to maintaining and developing raw coconut jelly production in association with environmental protection. Therefore,it is necessary to have a more suitable solution to guarantee low investment and operation costs for the small scale(almost family scale)production in poor rural areas in the developing countries such as in Mekong delta,Vietnam.

2 Conceptual framework

2.1 The available systems of waste prevention, reduction and treatment for bacterial cellulose production from coconut water

2.1.1 The development of models/systems for prevention and reduction of pollution in rural areas

The integrated model/system of agricultural production in rural areas is quite popular in the world as an integrated farming model(Therond et al.,2017),followed by integrating other non-agricultural livelihood activities to form multi-livelihood models. These integrated models bring many benefits such as reducing greenhouse gas emissions(Audsley and Wilkinson, 2014),increasing land use efficiency(Paolotti et al.,2016),deflation waste generation and additional income generation(Hai et al,2016)The multi-livelihood crop-livestock model has been known since the 1956s(Thomson and Bahhady,1995),and it has been extensively developed throughout the world, such as in an integrated system of chickens-olive trees farm(Paolotti et al.,2016), sheep-crop farming model(Rodr´ıguez-Ortega et al.,2017),soybean-livestock farming model(Esteves et al.,2018), pig-garden model(Zhejin Li et al.,2017). The garden-cattle farm type is one of the most popular models deployed in many regions of the world, typically in Southeast Asia (Baozhen Wang,1991), the tropical region(Stark et al.,2016), China(Komarek et al.,2015), Brazil(Alary et al.,2016),Africa(Rigolot et al.,2017),Mexico(Parsons et al.,2011),and in Europe(Peyraud et al.,2014).

On the basis of the house-garden model,the other models have also been developed. The method of forming the most popular integrated ecological models is to combine the garden with other specific livelihood activities in the same household (family area), such as the pond-garden livelihood model (Engle, 1987), garden-cattleponds model (Nhan et al., 2007; Yunlong and Smit, 1994), or in the combination with the forest area to form a garden-cattle-forest model (Costa et al., 2018). Another way is to combine the model with a biogas digester to create a garden-pond-cattle shed (cage)-biogas digester system (Baozhen Wang, 1991), or to combine it with craft production and other household production in order to form a full integration system consisting of 7 components: garden-pond -cattle shed-biogas tank-household toilet-craft workshop-wastewater treatment plant(Hai et al.,2016).

In general, the previous studies have indicated that the integrated eco-models in rural area have been developed on the basis of adding to and/or removing from the system one or more components (which represent the existing livelihood activities such as livestock, craft production, fruit and vegetable garden...,or the other objects in the household area such as pond, biogas digester, family toilet...),to the basic house-garden model,and then the authors have studied the metabolism between those components in the entire system/model (by analysing material and energy flows/balances) with aims to ensuring an ecological balance and minimizing the wastes/emissions.

2.1.2 The feasibility of the integration eco-models in the case of the production of bacterial cellulose from coconut water

Currently, the traditional integrated ecological models such as gardenpondcattle shed and/or the modified expanded models such as gardenpondcattle shedbiogas digester, or gardenpondcattle shed forest are commonly used to reduce rural pollution in Southeast Asia(Mohri et al.,2013). The water ponds in these models have been used only for the purpose of pollution reduction,but not for the full(complete)treatment of wastes,especially the wastewater,and the types of typical ponds used so far in the popular models are fish ponds,lotus ponds(lotus root pond) (Baozhen Wang, 1991). However, when the craft production component is added to the system/model,then the wastewater flow from the system needs to be treated following certain standards/requirements,which is normally not easy to perform under the rural conditions.

Therefore,the modification and improvement of the above-mentioned eco-models are the aims of this study,taking into account both the characteristics of craft production and the existing natural conditions of each household(family),in order to match with the wastewater treatment requirements and to reduce the waste generation as much as possible.

More modified models which are suitable for rural households having craft production are the models combining the components such as garden-cattle shed-biogas digester, and composting-house-craft production workshop-wastewater treatment plant (VACBNXT in Vietnamese) which have been developed by Hai et al.(2016) and applied successfully in a rice starch production craft village in the Mekong Delta, Vietnam. The diagram in Figure 1 shows the original VACBNXT model and its operation.

This model focuses on the metabolism among the components inside the model aiming at closing the loops of material and energy flows and maximizing the recovery of useful substances,leading to an increase in income for the households,and by that way,maintaining the effective operation of waste treatment facilities. This could help to overcome the barriers of operating costs,the most important barrier in waste treatment in rural areas in Vietnam in general and the Mekong Delta in particular(Hai et al.,2016).

Fig.1 Closed ecosystem“VACBNXT”for the craft villages in the Mekong Delta(Hai et al.,2016).(Earthworm farm and Livestock farm (C), Biogas plant and Composting plant (B), Crop (V), water pond(A), Craft production workshop(X),Living house(N),Wastewater treatment plant(T)).

Compared with the proposed framework of the VACBNXT model,the households producing coconut jelly under study has only 4 components: V (garden), A (pond), N (house), and X (craft production workshop),and there are 3 missing components: B (biogas digester), C(cattle shed/farm), and T(most of the households in the study area do not have a wastewater treatment plant). Therefore, in order to complete this model, the households have to invest in a biogas digester, cattle shed/farm and a wastewater treatment plant. However,the application of such a model for the case of raw coconut jelly production households may be faced with the following difficulties:

• The by-products of the raw coconut jelly process and the main juice from the BC (Bacterial Cellulose)fermentation may or may not be used for animal husbandry, the possibility to reduce costs under this aspect is still not evaluated.

• The investment for livestock shed/farm (C) and a biogas tank (B) to supply biogas for household needs and for boiling of coconut jelly will require a large number of animals (e.g., 40-70 pigs). Therefore,investment costs for C and T will be higher and may exceed the economic ability of the local households.

• The wastewater from the coconut jelly production having high N and P concentrations is combined with wastewater from the livestock farm,also showing high N and P concentrations,causing difficulties for the final wastewater treatment process. It would be then necessary to invest an additional system, such as a large wetland area would be required for an eco-oriented wastewater treatment. This type of process is certainly not suitable for the households having limited land area.

The above analysis shows that the VACBNXT model is not fully applicable for households producing bacterial cellulose from coconut water in the local households under study. The purpose of this study is,therefore,to propose a modified and propper model/system in order to overcome these difficulties.

2.2 Development of a conceptual framework for the system under study

Fig.2 The modified closed eco-model VACBNXCPT for craft production households in the Mekong Delta.

The production of raw bacterial cellulose from coconut water(often called raw coconut jelly) generates hardly resolved environmental problems such as polluted wastewater, the use of industrial chemicals (AS fertilizer,acetic acid), high energy usage for cooking etc. Due to the high concentrations of pollutants in wastewater,the investment costs of treatment systems for meeting the environmental standards are also high, leading to a number of difficulties when implementing wastewater treatment systems at the production households. To overcome these drawbacks, this study applies an ecological approach in combination with Cleaner Production techniques (e.g., on-site waste minimization and/or on-site waste recycling techniques) in order to form an integrated pollution mitigation model for the BC production process with the following main characteristics:

• Minimization at source: reuse and recycle of highly polluted wastewater in the same production process with purpose of minimizing concentrations of pollutants in the final wastewater (especially N, P),redesigning the cooking process to reduce energy consumption (gas) with the purpose of reducing the number of animals(pigs)necessary to produce enough biogas for the cooking demands,and replacing the chlorine(at disinfection step).

• End-of-pipe treatment: applying wastewater treatment technologies with low investment and operating costs;

• The ecological wastewater treatment and utilization systems (EWTUS)will be reconsidered and modified in this study with the purpose of being suited to the conditions of craft production in rural areas.

By applying these general approaches in accordance with the actual situation at each local household, one will build a sustainable production model for households which leads to environmental protection and reduction of costs when investing the wastewater treatment systems. The model framework of VACBNXT model,which is now modified into VACBNXCPT model for a proper application in local households with raw coconut jelly production,is depicted in Fig 2.

(1)Coconut jelly product for selling out to the market; (2)(10)The water from jelly soaking/washing tank is reused for production process; (3) (4) (5) (11) the wastewater flows such including processing wastewater, livestock wastewater, wastewater effluent from boiogas tank, and domestic wastewater are collected to the wastewater treatment plant; (6) (7)clean water after-treatment system is stored in the pond and served for further irrigation(watering)the garden,(9)(13)biogas from biogas digester(tank)is supplied to living house(for cooking and lighting purposes); (12) (14) production waste is used for feeding animals, (15) production waste is used as fertilizer for plantation in the family garden.

An improved pollution prevention and reduction model is proposed based on the optimal combination of factors/components V, A, C, B, N, X with the end-of-pipe treatment system (T) and cleaner production techniques available(CP-Cleaner production), called VACBNXCPT model. The model is set up targetting at waste reduction,waste treatment as required by given standards,and also at the reduction of investment and operation costs for the wastewater treatment plant, and possibly also aiming at gaining profits from waste reuse. The characteristics of the components in the integrated model are:

•V(garden):using wastewater after treatment (although the wastewater quality meets discharge standard,the concentration of nutrient such as N,P in this wastewater is still higher than in surface water)or use of the excess fluid from the fermentation of BC containing high N,S concentrations.

•A (pond):The pond will receive wastewater after the treatment system (T) for further treatment, and at the same time it serves as a water storage tank for irrigation purpose(especially in the dry season).

•C(cattle shed):Additionally, a pig shed with an appropriate number of cattle to provide enough biogas for the cooking jelly is designed , so that the amount of pig manure will be sufficient for the demand of biogas production, and there will be no need for investing an earthworm-raising system.

•B(biogas digester):The digester will be designed to a sufficient size for collecting livestock wastewater,production wastewater, and domestic wastewater, and supply enough gas for cooking BC as mentioned above.

•XCP:X is thecraft production workshop,where is the main activity for generating the household’s income.CP in this study is understood as cleaner production solutions such as reuse,on-site recycling,technology change,change of input materials,housekeeping practices,... which are involved in the craft production.

•N(house):house plays a central role in managing and operating the components V,A,C,B,X,T in the system.

•T:The wastewater treatment system(plant),T only handles a part of the treatment task,while the pond is designed to further complete the treatment of the wastewater.

•The jelly soaking tank:the tank for soaking the raw coconut jelly product after harvesting (a brick tank having a stiring system where the raw coconut jelly after harvesting and clean water are mixed well).

3 The context of the case study

3.1 The production of coconut jelly

The household (Mr Trung’s family) under this study is located in BenTre provincethe most famous and concentrated area for growing coconut trees, and for processing of coconut products in Vietnam. This family has a production capacity of about 5 tons of coconut jelly (un-pressed), or 500kg (pressed, the volume is reduced 10 times),the production time of each processing batch(from cooking to harvesting) is 10 days(incubated for 7 days). When operating stably, the product (5 tons) is harvested once in every 3 days. A typical production schedule for one family is shown in Table 1.

The production process of household is described in Fig 3.

The photos made at the processing site in Mr Trung’s family are presented in Fig 6 (Fig 6a-6e). Coconut water (stored in 30 litter plastic containers) is filtered by mesh and pumped into receiving tanks (3 m3). It is then pumped into the cooking pan where it is mixed with feeding water (or water-soaked in coarse jelly) at aratio of about 1:1. The sugar,vinegar and AS are added and the cooking is continued for about 15 minutes until the temperature of about 85-90◦C is reached,then the liquid solution is poured into the receiving tank and trays.

Table 1 Production schedule of the family.

The workers use a ladle to scoop exactly 1 liter (set by the ladle size) of the liquid solution after cooking and pour it into the trays,and then cover the trays quickly with newspaper,transfer them to the storage area for cooling down the jelly. One day later,when the temperature of the solution in the trays is about 30 degrees,the seeding is conducted. 15 trays are seeded out of one 1.5 l seeding glass bottle. After seeding,the liquid solutions in the trays are incubated for 7 days,after which the raw jelly is ready for harvesting.

The raw jelly in the trays is then removed,sorted and put into plastic containers(each container has a volume of 45 l).The possible defects on unsatisfactory jelly are removed(e.g.,mold marks on the product surface),after that the raw jelly is put into the containers (containing 1/3-1/2 water). After filling and soaking in water for a while,the jelly is taken out from the containers and packed into bags(about 40 kg for each bag),then the bags are pressed for removing excess water and collecting the final raw jelly product.

The material balance of the production process at the family is shown in Table 2. The data were collected from the current production at the family of Mr P.N.Trung.

3.2 The development of integrated pollution prevention solutions

3.2.1 Solutions for the formation of VACBNXCPT system at the family

Based on the method for setting up the system/model as presented in section 2, an integrated model was developed and applied at the household (family) of Mr. Pham Ngoc Trung, in Nhon Thanh commune, Ben Tre province (Mekong Delta,Vietnam)a typical family among ca. 100 families having coconut jelly production in the same craft village at the commune. The production capacity of raw coconut jelly at the family(after pressing for volume reduction of 10 times)is about 535 kg/batch,each batch period lasts for 3 days. The average amount of wastewater generated is about 5-7 m3/day. Some of the data about the family are: the living house(N)covers an area of about 100 m2;the area of craft production workshop(X)is about 400 m2;water ditch(Apond): there are 3 ditches,each with a width of 3m,with 2 ditches having 40-50m long and 1 ditch having 60-70m long,1.2-1.5m depth, the total area of all ditches is about 420 m2; garden area (V)is about 2680 m2 where grapefruits,lemons,and oranges are growing. Thus,the family owns in its area the components such as V,A,N,X.(garden,pond,living house,and production workshop).

In order to complete the VACBNXCPT model for the family, the following solutions are proposed to be conducted at the family area:

• Adding C:A livestock cage(shed)is newly added with the purpose to produce biogas for the production process of BC(and also for creating additional income for the household).

Fig.3 Diagram of BC production process from coconut water.

• Reuse of the defected raw coconut chips, as well as the excess water from the BC fermentation, for the demands of livestock activities(feeding the animals,and cleaning the cattle sheds).

• Collecting the garden wastes (leaves, tree branches, etc.) and use them as a raw material for producing biochar.

• Implementing B:the septic tank of the family is currently a self-infiltrated septic tank; the domestic and production wastewater is discharged directly into the environment. Therefore,the study proposed to build an anaerobic tank to collect and treat the wastewaters from living,production and animal husbandry, and the biogas generated can then be used for cooking.

• Implementing XCP: solutions for the workshop are: (1)-reuse water after pressing and soaking the raw jelly in order to reduce N, P,and COD loads of the wastewater, while reducing the amount of input materials for the process production of jelly; (2)-replacement of tray washing using chlorine by a disinfection tank using ozone; (3)-improving the cooking process, use a boiler instead of firewood(for cooking jelly),applying continuous cooking to reduce energy consumption,and also to reduce the amount of animals to a minimum number; and (4)-use water steam to disinfect tools in order to limit the use of chlorine. (5)-use of biochar for water purification before feeding it in the jelly cooking process.

Table 2 Physical balance of the production process.

• Implementing T:after coming out from the anaerobic tank B,the wastewater is passed through a biochar filter(biochar is produced from the garden wastes),and the wastewater flow is then leaded to the wastewater treatment system with floating plants (in the aerobic pond, the plants used are available at the local region);

3.2.2 Process diagram of integrated pollution prevention model VACBNXCPT at the P.N.Trung’s family Based on the specific features of the family, this study proposes an integrated pollution prevention model to minimize emissions into the water environment for the given family as shown in Figure 4.

3.3 Implementing cleaner production solutions and eco-oriented wastewater treatment system

Some of the solutions in the proposed model, as shown in Figure 4, have been implemented/demonstrated onsite at the family’s area under study, e.g.,(1)the coconut jelly soaking water has been reused; (2)replacement of chlorine for tray washing by a dia sinfection tank using ozone;(3)use of biochar for water purification before feeding in jelly cooking process;and(4)installing of an eco-oriented wastewater treatment system(as described right below).

Fig.4 Diagram of an integrated pollution prevention model VACBNXCPT for the aqueous environment at the Mr. Trung’s family.

Fig. 5 Diagram of the wastewater treatment system implemented in practice at the household. (1)-oil separation tank;(2)-stabilization tank;(3)-water pump;(4)-anaerobic biofilter tank with(5)buffer material;(6)-filtering tank using biochar as a filtering material(7);(8)-water pond with floating plants(9);(10)-disinfection tank or water receiving pond for further watering;(11)-going to the receiving source.

The wastewater treatment plant (WTP) has a treatment capacity of 7 m3/day (wastewater discharged from one batch is 20.2 m3, the washing cycle is repeated every 3 days, resulting in a total of 21 m3/3 days for both domestic and processing wastewater resulting in 7 m3/day on average). The process diagram as shown in Figure 5 is designed to operate continuously 24 hours/day. In Fig 5:the oil separation tank(1)with a volume of 2.8 m3;the stabilization tank(2)with a volume of 18 m3,the anaerobic biofilter tank(4)having buffer material(5)with a volume of 10.5 m3, the filtering tank (6) using biochar as a filtering material (7); the pond (8) with floating plants (9) with a volume of 50 m3, the disinfection tank (also as a water receiving pond for further watering)(10) with a volume of 5 m3. The photos made at the system in Mr Trung’s family are presented in Fig 6 (Fig 6f-during construction, and 6g-during system operation).

Table 3 The quality of wastewater at the stabilization tank after applying the reuse of soaking water for purpose of cooking the jelly.

Table 4 The quality of effluent wastewater before discharging into receiving source(tank 10,in Fig 5).

3.4 Evaluation on the effectiveness of the applied sollutions

3.4.1 Evaluation of the effectiveness of reducing pollution load when applying the reuse of jelly soaking

and pressing water for cooking process

The family has implemented the reuse of jelly soaking and pressing water for the cooking process (1 liter of coconut water plus 2 liters of water after soaking the jelly). The total amount of water after soaking jelly is about 7 m3/batch,the amount of additional coconut water is about 3.5 m3in order to create 10.5 m3of nutrient solution for the process of producing jelly. After reusing the soaking and pressing water of raw jelly,the family’s wastewater is now generated mainly from the process of washing the trays.

After the implementation of this measure (reusing the soaking water), the quality of the wastewater was checked again,the results are given in Table 3. The reuse of soaking water in each batch helped to reduce more than 90% of pollutants in the wastewater (e.g., 27 kg COD, 21.4 kg BOD5, about 7 kg N, 113 g P and 28 kg). The data of wastewater quality of the sample taken at the stabilization tank after applying the reuse of soaking water for the purpose of cooking the jelly is given at the table 3 below.

3.4.2 Evaluation of the treatment efficiency of the wastewater treatment system

The area of the biological pond used for wastewater treatment (water pond 8 in Fig. 5) is a ditch with a total length of 30 m.The treatment capacity of the pond is calculated based on the discharge requirement(according to the local regulations of the province,the wastewater effluent must satisfy the“Vietnamese national standard for wastewater discharge” (QCVN 40:2011, column B),and the appropriate treatment technology before entering the pond (anaerobic tank with buffer material) was selected, as shown in Figure 5. The quality of effluent wastewater from the system after anaerobic and desinfection tanks is presented in Table 4.

3.4.3 Preliminary economic evaluation for the integrated system

The use of biochar for filtering the water supply before the cooking process has helped to purify the water,and also to reduce the heating demand for cooking the jelly. This application has supported in reducing the fuel cost for heating the incineration oven at the jelly cooking step by 10%, corresponding to 1,500,000 VND or 64.4 USD/month (the cost for firewood is 15,000,000 VND/month without the indicated change in the process, or 13,500,000 VND/month after applying that change).

The use of ozone for tray disinfection instead of using chlorine for the same purpose has helped the family to reduce the production cost of about 10,000 VND or 0.43 USD/day(before applying this method,the family used 1 kg of chlorine for every 2 days on average,amounting to 40,000 VND or 1.71 USD/kg for tray disinfection).The family is now using 2 ozone generating instruments, used once in every 2 days, 4 hours each time, the instrument’s capacity is 35 W,electricity cost is 1,600 VND or 0.069 USD/kWh).

Besides that,the investment cost for a wastewater treatment system at the family when applying the model is only 10-20%compared to that without applying the model/system: the original costs of the treatment system for organic matter,N,and P,and the sulfate removal system are estimated to be about 170 million VND for each,therefore the investment cost of the original complete system was about 340 millions VND;the total investment cost for the system in Fig.5 is about 40-60 millions VND,or about 1,700-2,500 USD,and this price is acceptable for the local families. If the integrated solutions are not applied,the operating cost is estimated at 23,500 VND or about 1 USD/m3(of which the operating cost of the sulfate reduction chemical system is about 19,000 VND/m3of waste water,the remaining items are estimated at 4,000 VND/m3of wastewater),while the operating cost of the wastewater treatment system after applying integrated solutions is only about 1,000 VND/m3of wastewater.

3.4.4 Overall evaluation of the effectiveness of the proposed system

The integrated pollution prevention and treatment system proposed in this work for raw coconut jelly production meets the requirements of the State of Vietnam. In addition,when applying this system,the main issues such as wastewater treatment technology, the investment and operation costs of wastewater treatment plants have been resolved due to the elimination of hardly-removal pollutants such as N,P and SO42-,thus the system has high applicability at the local area. Although this system has low investment and operating costs,it still faces many difficulties when applying in practice in the Mekong Delta, Vietnam. The local people are still worried about electricity costs for operating the wastewater pump(from the stabilization tank into the anaerobic tank).

Another big obstacle when implementing the proposed system may come from the unstable market situation for the coconut jelly product. Sometimes the processing must be stopped for some days, and that will affect seriously the normal operation and the efficiency of the wastewater treatment system. It will be a task for the local government to enhance a stable selling market for these small businesses in order to stabilize the output and production of coconut jelly,ensuring the sustainable development of the craft profession in Mekong delta.

3.4.5 Other potential technical solutions for future application

In addition to the above-applied solutions,other potential solutions which can be applied to complete the system are suggested as follows:

Reuse of the excess liquid solution from the production of BC as a source of liquid fertilizer for plants.The remaining liquid solution after the fermentation process of BC has a volume of about 27,7 % of the total medium solution used to ferment BC (equivalent to 1.688 kg/batch). The content of N used for making the fermentation medium of BC is mainly taken from AS,and with an AS concentration of about 1.5%,equivalent to a N concentration of 0.3% and Sof 0.35%. In which N is a plurality element and S being an intermediate element necessary for plant growth. Therefore,the use of the liquid solution from the BC fermentation will have a positive impact on crops,and help to reduce the amount of N and S fertilizer.

Fig. 6 The photos made at the Mr Trung’s family: (a) Plastic trays used for fermentation/incubation of raw jelly; (b)Microorganism species used for jelly fermentation are growed in the plastic bottles,each bottle after use has a piece of BS as showed in the above photo;(c)The coconut water is pouring into plastic containers(each container has 30 kg coconut water);(d)Cooking oven by using firewood(The quantity of firewood and ash are weighted before and after each cooking batch);(e)Pooring the nutrient medium into the trays for further fermentation;(f)The construction of wastewater treatment system at the Mr Trung’s family; and (g) The operation of eco-oriented wastewater treatment system at the Mr Trung’s family.

Fig. 6 Continued.

Reuse of BC chips(debris)as feed for pigs.The BC is nano cellulose,so it can be considered as supplementary source of fiber and vitamins for livestock animals,especially vitamins B1,B2 and C.The amount of BC’s chips at the household is about 245 kg/batch on average (with 90% moisture content), and it is an alternative source of fiber for livestock animals. Implementing this solution will help to convert BC waste into meat as a food of high quality. A research has been done byElferink, Nonhebel, and Moll (2008)on a number of food residues and waste products from food processing industry such as vegetable oil production, potato processing industry,sugar production industry,etc. with the purpose to use them as feed for animals,and the results showed that the use of livestock by-products will reduce environmental impacts when compared with using industrial feed while meat quality is not affected.

Use the livestock manure for biogas production and provides biogas for cooking of medium used for BC fermentation.In order to increase efficiency, it is possible to increase the ecological feature of raw coconut jelly production process by using draff water from traditional liquor production. This replacement will reduce production costs by 67%(Wu and Liu,2013). This solution has many potential applications because BenTre is a province with many traditional wine-making villages such as Phu Le and Binh Phu. In addition, this solution will also reduce the competition of coconut water between producing fresh coconut and coconut jelly.

Replacement of the incineration oven using firewood by installing a new boiler.The jelly cooking step deals with many problems requiring improvement,in which the highest priority is given to reducing fuel cost for jelly cooking. The use of a boiler instead of using the traditional incineration oven using firewood could help to reduce this cost up to 50%.

4 Conclusions

This study proposed and demonstrated an integrated eco-model/system to minimize the environmental impact of raw coconut jelly production, an improved and modified model of VACBNXT to VACBNXCPT.The system and solutions having been implemented showed the advantages of integrated pollution prevention, exploiting the advantages of existing natural conditions at the families, used them to form the eco-oriented end-of-pipe wastewater treatment system which satisfies all the of environmental standards at low investment and operating costs, and also simple operational skill. At the same time, this system also contributes to meet the legal requirements on environmental protection and development of the coconut jelly production craft profession in the country. This model shows that in order to achieve a high efficiency,the families should apply all the suggested solutions simultaneously, otherwise the components in the system will not be in a balanced state, and thus the efficiency is not as desired (for example, if the jelly soaking water is not reused, then the components B and T will not work effectively).

Acknowledgments

This research was funded by the Vietnam National University of Ho Chi Minh City(VNU-HCM)under the grant number KHCN-TNB/14-19/C25. The authors also thank the Asean-European Academic University Network(Asea-Uninet) for financial support to collaboration between IER(VNU-HCM,Vietnam) and IPPE(TU Graz,Austria)to implement this study.

List of abbreviations

AS:Amonium sulphate

BC:Bacterial cellulose

NPP:Nitrogen-phosphorus-potassium fertilizer

MDF:Medium Density Fiberboard

HDF:High Density Fiberboard

VND:Vienam Dong(the Vietnam’s currency,1 USD=23,500 VND(September 2019)

QCVN 40: 2011/BTNMT:National Technical Regulation on Industrial Wastewater in Vietnam