Vermifiltration

Vermifiltration is a process and technology to treat domestic, urban and agroindustrial wastewater using earthworms and is developed currently in vermifilters.Is a branch of vermitechnology and, consequently, an ecological engineering and environmental engineering tool. The process reduces organic matter, increase mineral nutrients and eliminates pathogens and helminth eggs in wastewater. It can work as primary, secondary and tertiary treatment however, in wastewater treatment, is frequently recognized as a secondary treatment technology.

Definition and overview

Vermifiltration was first advocated by researchers at the University of Chile in 1992 as a low cost sustainable technology suitable for decentralised wastewater treatment in rural areas. Vermifiltration is based on the same oxidation reactions, biodegradation and microbial stimulation by enzymatic action also present in vermicomposting and in trickling filters. Dissolved and suspended organic and inorganic solids are trapped by adsorption and stabilization through complex biodegradation processes that take place in the filter packing, being subsequently used by microorganisms.^[1] Vermifiltration has been shown suited to treat municipal wastewater,^[2] rural domestic wastewater,^[3] brewery and daily wastewater,^[4] petrochemical wastewater,^[5] and herbal pharmaceutical wastewater.^[6] As in vermicomposting, in vermifiltration, epigenic earthworms convert the organic matter in wastewater into a suitable matrix filter – the vermicast, with the potential to be applied on soil. Vermifiltration is a bio-oxidative process in which earthworms interact intensively with microorganisms within the decomposer community, increasing the stabilization of organic matter and greatly modifying its physical and biochemical properties,^[7] combining filtration processes with vermicomposting techniques. The central concept behind vermifiltration is that microorganisms perform biochemical degradation of waste present in wastewater, while earthworms regulate microbial biomass and activity by directly or/and indirectly grazing on microorganisms.^[8] Vermifiltration applications include small pilot-scale tests, households and small Wastewater Treatment Plants (WWTP), opening new opportunities for treating domestic, urban wastewater and industrial wastewater due to the low cost and sustainable nature.^[1][9]

Earthworms importance

Earthworms represent the major animal biomass in most terrestrial temperate ecosystems,^[10] being an important group of soil fauna whose activities contribute strongly to the development of soil structure, nutrient cycling and soil fertility. In vermifiltration earthworms mechanical action creates aerobic conditions inside the reactor which help prevent the formation of odors. Besides, earthworms increase bacteria growth and digest the solids in wastewater.

Reactors used

Vermifiltration is made in a reactor called vermifilter, a passive aerobic bioreactor. Vermifilters offer treatment performance similar to conventional decentralised wastewater treatment systems but with potentially higher hydraulic processing capacities.^[11]

Wastewater is applied by drop by drop over an organic filter packing, normally sawdust, shredded food, shredded branches or, in particular cases, vermicompost. Vermifilters should have an organic packing and an inert section – made usually with a layer of quartz sand and a layer of gravel. Construction waste could also be used in substitution of gravel. Also, recycle plastic sawdust can be a good substitute for quartz sand. A stainless steel mesh or a geotextile fiber (or both) should separate physically these layers from each other.

The structure has also an equalizer, where the treated wastewater is collected and recirculated. This structure could be installed within the system or separately, but always be installed on the bottom. A vermifilter can me made or assembled in PVC, PP, HDPE, bricks, cement blocks or even concrete. Typical household vermifilters are made usually by reusing PVC containers even if concrete rings could also be used. Sustainability is a core aspect when sizing vermifiltration reactors. When treating domestic wastewater, it is always to reuse materials rather than use raw materials. Consequently, in filter packing, quartz sand and gravel are usually substituted by recycled plastic sawdust and ceramic waste, respectively. As in wormcomposting – which does not require too much raw materials to make wormeries or vermidigesters, this is one of the advantages of sizing vermifilters. In the context of urban and agroindustrial wastewater treatment, vermifilters are normally made with bricks, cement blocks or concrete.

Process description

When a slope can be made, untreated/raw domestic wastewater is first transported by gravity from the original facilities to a septic tank where a first settling and digestion of solids occur. This should be called the primary treatment since occurs solids sedimentation and digestion. Moreover, the fact that earthworms could digest the solids remaining (near (60% to 70%), could characterize the process also for primary treatment but normally, the septic system will prevent any clogging situations in vermifilter. When no slope can be made, piping from the septic tank should be solved. Usually, at domestic and urban scale 1 m² of filter surface area can treat near 2.5 m³ of wastewater per day (equivalent to a flow production of 20 inhab.) usually with a 2 hour hydraulic retention time.

When treating wastewaters with high organic concentration - normally from agroindustries, wastewater recirculation from the equalizer to the top of the vermifilter promotes organic load dilution and avoiding that the population of earthworms can decay due to is death. Depending of several specific conditions, a vermifilter could have removal efficiencies for Biochemical Oxygen Demand (BOD₅) more than 90%, Chemical Oxygem Demand (COD) more than 85%, Total Suspended Solids (TSS) more than 98% and NH₄⁺ more than 75%. In specific conditions, is possible to achieve a elimination of faecal coliforms until 2.0 Log₁₀ of Most Probable Number (MPN) per 100 mL⁻¹.^[12]

On-site domestic treatment

In developed countries, a significant fraction of the population still does not have adequate wastewater services (sewage drainage and wastewater treatment) available. In the non-developed countries, this problem is still more severe, leaving this situation being the most typical in these societies. In developed and non-developed countries, the lack of an adequate wastewater service is entirely on rural areas. As an example, for a typical household with 4 inhabitants it will be required an area of 0.104 m² per person or a total surface area of 0.42 m². Soto (2000) predict that the surface area per person should be 0.1 m².

Urban treatment

Vermifiltration has been shown suited to treat urban municipal wastewater (Soto and Toha, 1998). Urban treatment requires larger surface areas when compared with domestic treatment. Even so, when compared with traditional lagooning systems, vermifiltration requires less surface area per inhabitant. RECYCLAQUA^® is a French project developed in 2005 to serve a community of 2,000 inhabitant equivalents at Combaillaux, France. There sludge produced is almost entirely from sieving pre-treatment (< 2mm), being treated locally by vermicomposting. The system requires 0.25 to 0.5 m^-2 per p.e. and use a minimal amount of energy. It also had a real capacity to absorb major fluctuations in hydraulic load and reach actually all the EU quality regulations for discharge. Bidatek^® is a Spanish company located in San Sebastián, who operates in vermifiltration market. It has also a delegation in Brazil. His main work is related with development, sizing and construction of vermifiltration units to treate domestic, urban and industrial wastewater. The process has the following efficiencies: BOD₅ (95%), TSS (95%), TN (60 to 80%), TP (60 to 70%), total coliforms (99%).

Agroindustrial treatment

Wastewater from agroindustries has normally higher contends of BOD₅, COD and TSS comparing with domestic and urban wastewater. Even so, vermifiltration had proved to be viable solution to reduce those parameters. As an example, (Sinha et al., 2014) studied the vermifiltration of wastewaters from Fruit Juice Processing Industries in Brisbane. They are high in BOD and COD values. This type of wastewater had 1340 mg L^-1 of BOD₅ and 2730 mg L^-1 of COD, respectivelly. Removal efficiencies were 99,8% and 95.9%. Sinha and Bharambe (2007) also studied the vermifiltration of brewery wastewater which have very high BOD₅ and TSS concentration e.g. 6780 mg L^-1 and 682 mg L^-1. Earthworms removed BOD₅ by 99% and TSS by over 98% with an hydraulic retention times HRT of 3-4 hours. In rural areas, treatment of liquid manure can result in the production of ammonia, nitrous oxide and methane.

Industrial treatment

Sinha et al.,(2012a) studied vermifiltration of wastewater obtained from automobile service industry. This wastewater contained a mixture of aliphatic and aromatic volatile hydrocarbons (C10–C36) and organochlorines. The aromatic fraction mainly consisted of PAHs and is more toxic and persistent than the aliphatic part. Earthworms not only tolerated and survived as were also responsible by wastewater treatment. Dhadse et. al., (2009) studied the vermifiltration of herbal pharmaceutical wastewater, which has very high BOD₅ (11,200-15,660 mg L^-1), COD (21,960-26,000 mg L^-1) and TSS (5,460-7,370 mg L^-1). BOD was removed by 90–96% and COD by 85-94%, using a two day hydraulic retention time. Heavy metals were also removed and no sludge was formed.

Management and maintenance

Air temperature, moisture, BOD₅ and COD concentration in effluent, flow rate, hydraulic retention time, organic loading rate, evapotranspiration and precipitation are key parameters who will influence vermifiltration process and efficiency, since they could contribute to change the chemical and physical properties of the filter packing within the vermifilter and consequentially earthworm survival.

Environmental beneffits

Vermifiltration has been shown suited to treat municipal wastewater (Soto and Toha, 1998), rural domestic wastewater (Wang et al., 2011), brewery and daily wastewater (Sinha et al., 2007; Sinha et al., 2008), petrochemical wastewater (Sinha et al., 2012), herbal pharmaceutical wastewater (Dhadse et. al., 2010). Also:

• Low maintenance: the system needs only an annual check-up. Although maintenance requires some basic knowledge about vermifiltration systems, it does not require the skills to operate with high technology systems.
• Noise free: systems built on a hill do not require any pumps which make noise. Even those systems that require pumps are almost noise free as the pumps run only a couple of times a day.
• Independence: System is not connected to the wastewater system provided by your municipality. This is especially beneficial to farmers and customers in remote locations for whom it is difficult or expensive to be connected to the central water treatment facilities.
• Quality: Treated wastewater has higher quality than the treated wastewater from the conventional domestic and large Wastewater Treatment Plants.
• Environmentally friendly: The system is virtually odorless, noiseless, and requires minimal daily or even monthly maintenance from the client.
• Cost Effective: By requiring only 5-20% of the energy and none of the chemicals required by traditional processes, a vermifilter reduces the carbon footprint and overall wastewater management expenses.
• Zero Sludge: Since the system does not produce any sludge, eliminates the need for clients to contract waste haulers commonly used for sludge management.
• Reuse water in households, gardens agriculture will reduce pressure on aquifer from which we source fresh water and save costs in having to pay for water from the central grid or pumping groundwater. Simultaneously, the presence of nutrients in the wastewater resulting from vermifiltration system will have nutrients that reduce commercial fertilizer expenses.
• Vermifiltration will be beneficial to households and farmers in almost any condition in which water for irrigation is required.
• In general, wastewater treatment systems do not provide for the removal of significant amounts of nitrogen or phosphorus (USEPA, 2007 ). Vermifiltration helps to promote nutrient cycling.

Irrigation and nutrient cycle

The reuse of wastewater has been successfully used for the irrigation of a wide array of crops, and increases in yields ranging from 10 to 30% have been reported (Asano and Levine, 1998). Normally, treated wastewater still contains impurities, as it may present a variety of concerns. However, treated wastewater using vermifiltration is normally constituted by less than 5.0 mg L-1 of TSS (ref).

Economic aspects

Sizing a vermifiltraion unit should involve a strong information about the construction costs, operation and maintenance costs and dismantling costs. Constructon costs should include raw materials, equipment, energy, human labour and machinery. Partial construction costs should include all the systems that origin the vermifiltration unit: inspection box, septic tank and vermifilter. Operation should predict energy consumption when pumping is needed and when wastewater recirculation in vermifilter is present. When treating urban wastewater, costs are a significant support to select the best technology between the several solutions available. According to Sinha et al. (2014), the capital and operating costs are hence much less by over 70% than other sewage treatment plants (STPs) and is very suitable for developing nations including India where STPs often remains idle due to shortage of power.

See also

References

External links

At Wikiversity, you can learn more and teach others about Vermifiltration at the Department of Vermifiltration

• What is "ecological engineering"? Webtext, Ecological Engineering Group, 2007.

Organizations

• American Ecological Engineering Society, homepage.

Scientific journal

• Ecological Engineering since 1992, with a general description of the field.
• Landscape and Ecological Engineering since 2005.