Grass filtration in parallel with VFCW technology for community wastewater treatment through the king's initiative nature-by-nature process

An increase of Thai population has been exploded from 1950 to 2013 which was approximated 0.8 million per year. Undoubtedly, forest lands were trespassed in using for traditionally growing agricultural crops with without care for keeping soil in place which could be the basic cause of losing plant nutrients. The previous statements resulted to gain less productivity of growing crops that made farmers poor and uneducated persons to reside such infertile land. Surely, they moved into the city for better job opportunity that made dense-populated community and becoming the huge point sources of wastewater, solid wastes, visual pollution, air pollution, and social problems. Among those worse environmental problems, wastewater has been taken in the most serious problem in causing stream pollution around the Kingdom of Thailand. Anyway, field observation revealed that wastewater of these water sources have seriously been polluted from their settling big cities. Besides, the industrial factories which were localized close to the water sources could make worse water pollution in everywhere around the country due to the direct drainage the effluent from factories without treating. Also, the amount of wastewater was about 85% of total consuming water, the other part permanently trapped by equipment and also small drops surely evaporate to sky. In other words, whenever amount of clean water is used for any purpose, those amounts of water will become to wastewater approximately 85% which drains into rivers and another 15% being trapped by equipment and water users. Anyhow, the previous studies found that if useable water was about 200 L/person/day by city residents, 50 L/person/day by progressive villagers, and 30 L/person/day by remote villagers. Then after, these amounts of household wastewater have to release to the stream channels at least 70% of total wastewater, and becoming stream pollution. Obviously, wastewater as drained from communities and cities is normally contaminated with mostly organic wastes that becoming important part of stream pollution.

In the tropical areas, the community wastewater treatment should employ the constructed wetlands due to long-period sunshine, various species of aquatic plants available, and well-distributed natural wetlands. In fact, VFCW technology is preferred to HFCW (horizontal flow constructed wetland) technology because of longer soil-profile depth for screening and adsorbing positive and negative charges of bigger particles and dissolved organic and inorganic waste particles while vertically flowing down but it depends on soil-pore-size distribution. With those requirement, soil texture plays vital role in functioning on not only vertical flow rate of wastewater from sunken surface soils down to the bottom throughout sand and gravel levels before passing through the appropriate pipe-hole sizes, but also on the wastewater concentration. Evidences from the previous researches were confirmed that VFCW technology could be efficiently applicable on the BOD concentration more or less 200 mg/L (LERD 1999; Molle et al. 2008; Sklarz et al. 2009; Zhu et al. 2012).

It is explained that photosynthesis is the process which plants and some organisms use the solar energy from sunlight to produce glucose/sugar, (which cellular respiration convert into ATP the fuel used by all living things). Normally, the photosynthesis process uses water and CO₂ then releasing the oxygen in to the wastewater for aquatic plants or in to the atmosphere for in-land plants. Principally speaking, photosynthesis is the process in which plants naturally convert energy from the sun into chemical energy that can be used to fuel the organism activities (Hammer & Bastian 1989; Botkin & Keller 2005; Keddy 2010). Another nature-by-nature process is named as thermo-siphon process which refers to the circulation of liquid, air/gases and volatile gases in heating and cooling applications without the necessary of a mechanical pump. Direct solar radiation from sun to wetlands makes surface water heating/ warming by using heat on the nearly surface that causing water evaporating from surface in which surface water becomes cooler and denser to force it sinks down to the bottom (Arneth & Stichlmair 2001; LERD 2012). The concerned in-depth explanation would be concentrated on the fact that heating surface water with specific heat of water (583 cal/g) to make it cooler and heavier enough to sink down then replacing by moving up with the warmer water from the bottom. At the same time, the above oxygen (air) penetrates in space among molecules of cooler water and sinks to the lower level and finally to the bottom (not more than 3 m) (LERD 1999, 2012). Therefore, thermo-siphon is the process governing oxygen circulation by heating and cooling on surface water of wetlands for energy supplying to bacterial organic digestion process without using the necessary machines as mentioned by Mirmov & Belyakova (1982) and Arneth & Stichlmair (2001). The last nature-by-nature process for supplying oxygen to bacterial organic digestion process is placed on the thermo-osmosis which is the process of a fluid (wastewater) through a soft membrane under the influence of a temperature gradient that transforming to thermal forces and pressure forces in consequence. This principles can be applicable to transfer the oxygen from atmosphere to parenchyma cells (spongy cells) by photosynthesis process throughout the aquatic plant vessels to the root zones (rhizomes) which are the habitat of organic digesting bacteria as found by Denbigh & Raumann (1952), Bearnan (1957), Grosse (1989) and Grosse & Bauch (1991).

The products of bacterial organic digesting process are exactly identified as plant nutrients and some toxic chemicals as accumulated in soils for growing submerged aquatic plants (such as typha, cyperus) and dispersing in treated wastewater for growing phytoplankton (Hammer & Bastian 1989; Jenssen et al. 1994; Ahn & Mitsch 2002; Stottmeister et al. 2003; Maine et al. 2006; Liawpatanapong 2008; Cui et al. 2010; Suchkova et al. 2010). The balancing condition is really needed to harvest the submerged aquatic plants by clear cutting of the zero-growth rate of the oldest plants with leaving the stem about 30 cm height, and to consume the herbivore fishes together with zero-growth rate of biggest size. The said concept has been shown in success of organic wastewater treatment under the principles of biological processes through both the VFCW and HFCW technologies as resulted from the previous researches Juwarkar et al. (1995), Stottmeister et al. (2003), Kayser & Kunst (2005), Cui et al. (2010) and Zhu et al. (2012). To support the said principles, the wastewater treatment efficiencies found were varied from 85 to 95% for Chemical Oxygen Demand (COD), BOD, Total Dissolved Solids (TDS), Suspended Solids (SS), Dissolved Organic Carbon (DOC), Dissolved Organic Phosphorus (DOP), Dissolved Organic Nitrogen (DON), NH₃-N, color, coliform and fecal bacteria; 80 to 90% for sulfate, TKN, EC, alkalinity, acidity, and organic compounds (Nopparatanaporn 1992; Juwarkar et al. 1995; Maine et al. 2006; Molle et al. 2008; Khan et al. 2009; Sklarz et al. 2009).

From the problem-based polluting on surface wastewater in the populated community, King of Thailand has royally initiated the community wastewater treatment systems by VFCW technology through nature-by-nature process which is the simple technique and low expense or non-payment if local materials to be useable for assembling the mentioned technology. Summarily speaking, the objectives of research will be focused on the applicable efficiency of VFCW technology in parallel with phytoremediation techniques by growing grasses and its non-toxic products for feeding the local livestock.

However, Phetchaburi municipal wastewater was drained into all 3 VFCW experimental units for 5-day stagnation and another 2-day releasing, and repeating this process every 7 days until Star, Kallar, and Coast couch were met its useful life for clearly cutting from the VFCW units. If the rhizomes were kept in place, the new shoots of those grasses could be surely coppiced as seedlings and fully growth in parallel to the wastewater treatment efficiency in the VFCW units. Research experiences found that the rhizomes could be useable up for the fourth rounds but high efficiency should be useable approximately 3–5 years, depending on the organic concentration and types of wastewater sources.

The effluent samples were taken at the end pipes and stabbed columns every 7 days in order to designate the efficiency of CW-aquatic plants for color rectification. The water quality indicators are needed from analyzing treated wastewater samples such as COD, BOD, TDS, SS, color, pH, temperature, and ammonium – nitrogen. Accordance with the experimental research operation was conducted during 1995–2010 (15 years); the presented data here were the averaged values. Also, the height growths on the specified stems of Star, Kallar and Coast couch grasses were measured every seven days in order to determine the usable age for cutting off the VFCW units for encouraging higher efficiency of wastewater treatment from the shoots.

Owing to the influent for VFCW technology together with growing grasses obtained from the Phetchaburi municipal that might have some heavy-metal contaminates. The toxic contaminants in influent and effluent through VFCW technological plots were intensively analyzed and found the quality indicators as shown in Table 5. The pH value did not evidently show any change of influent to effluent among grass species but drastic change in BOD, TKN, TP, and TK (Table 5).

This would be the causes their transforming to dissolved organic matters as up taken in rapidly growing of Star, Kallar, and Coast couch grasses and their accumulation in grass tissues. There were some parts of organic forms to escape from the VFCW technical units as volatile gaseous chemicals; and some parts might be precipitated down to the VFCW technical unit beds (Boyd & Vickers 1971; Hammer & Bastian 1989; Ye et al. 2001; APHA AWWA WEF 2005; Botkin & Keller 2005; Kayser & Kunst 2005; Liawpatanapong 2008; Melian et al. 2008; Cui et al. 2010; Keddy 2010; Gikas & Tsihrintzis 2012), It would be noted that the Star and Coast couch grasses showed higher potential in community wastewater treatment efficiency than Kallar grass but their values of treating power were not so much different each other. Remarkable observation had to pay more attention on influent of VFCW technical units that was treated the effluent from Tayang collection pond belonging to Phetchaburi municipal (a case study of BOD as pertained more than 200 mg/l) by 18.5 km HPDE pipe to lower down to 18 mg/l because of high treatment rate of anaerobic process which made low rate treatment efficiency as seen in Table 5.

Accordance with containing some heavy metals (Pb, Cd, Hg as example) were contaminated in both treated wastewater and sludge (sediment). It is very necessary to analyze them in influent and effluent, the results found them very low contamination but those grasses showed their eligibility in heavy metals, especially when their age at 45-day growth as the same findings of treating BOD, TKN, TP, and TK due to meet highest treatment efficiency at age of 45 days of Star, Kallar, and Coast couch grasses (Zhu et al. 1999; Pulford & Watson 2003; Hadad et al. 2006; Chunkao 2010; Chunkao et al. 2012). In other words, the harvesting age at 45 days was not only reached the maximum treatment efficiency as well as maximum grass biomass but also kept away from heavy contamination.

The research was taken the originated data as collected for 15-year period (1995–2010) for evaluating community wastewater treatment applicability of Star, Kallar, and Coast couch grasses through VFCW technology in parallel with determining appropriate harvested cutting as well as nutrient condition for feeding the livestock.

There were three VFCW technical units with the size of 5 m width, 100 m length, and 100 m depth in parallel with filling gravel 5 cm, sand 10 cm and soil 30 cm for gravel, then following by growing Star, Kallar, and Coast couch grasses with the 25 cm spacing. The grasses have to be taken with care until their height getting to the establishment period (about 3 weeks) before draining Phetchaburi municipality (community) wastewater into the VFCW units at the level of 30 cm from the soil surface. Then after, the stored wastewater in VFCW units were treated by alternating stagnant for 5 days before releasing and 2 days releasing through soil-sand-gravel profile to the bottom and flowing-in pipe-holes.

The treated wastewater as drained out from the VFCW technical units was collected for analyzing water quality indicators such as pH, BOD, TKN, TP, TK, Pb, Cd, and Hg.

Results found the Star, Kallar, and Coast couch grasses can be applicable for treating all-water-quality indicators, and also providing edible grasses for feeding livestock with very less toxic contaminants.

The appropriate age for harvested cutting was found at 45 days in which the productivity of Star, Kallar, and Coast couch grasses were provided in fresh-weight 485.8 kg/ha, 484.6 kg/ha, and 460.8 kg/ha, respectively. In other words, one VFCW technical unit (500 m²) can produce grass biomass about 60 kg that may be enough to feed the livestock for 1 day.

This research received financial supports from The King's Royally Initiated Laem Phak Bia Environmental Research and Development Project, Chaipattana Foundation, Thailand and Eco-science Community Research Group, Faculty of Environment, Kasetsart University.