Industrial Wastewater Treatment
Oenological Wastewater Treatment System for Wine Cellars
Precast reinforced concrete
for wastewater characterized by a high content of grape skins, berries, pomace stalks, leaves, etc...
Introduction
The purification treatment of wastewater from wineries and cellars is a difficult and complex problem to address, the issues of which are mainly linked to the marked seasonality of processing (concentrated largely over 2–3 months per year, i.e., the grape harvest and winemaking period) and the high organic content of the discharges.
These wastewater streams are also characterized by a high content of grape skins, berries, pomace stalks, leaves, etc., which must necessarily be removed upstream of the treatment.
The transformation of grapes into wine obviously has a strong seasonal nature; the use of water and the consequent formation of effluent derive, in fact, substantially from the washing operations of the equipment (crushers, destemmers, presses, etc.), containers (collection tanks, fermentation and filling vats, etc.), and premises (floors, yards, etc.) according to the following phases and periods:
- harvest-crushing (September–October);
- racking (May–June);
- bottling (February–April and October–December).
During the rest of the year, discharges mainly derive from the washing operations of machinery, floors, and product containers, and the daily hydraulic load is reduced by up to 5 times compared to the peak period.
This large quantity of liquids is not inherently polluting, as it mainly contains non-toxic organic substances, but it still has a negative environmental impact, also because it is produced in limited time periods.
Attention has been focused primarily on small and medium-sized wineries, the most common in the study area: the average was 400 quintals (40 tonnes) of processed grapes per year.
The objective was to evaluate the possibility of an agronomic use of these effluents, after stabilizing them through storage under anaerobic conditions (i.e., in the absence of oxygen and thus not in contact with the air).
From one hectare of vineyard, approximately 80 to 130 quintals (8 to 13 tonnes) of grapes are obtained, with an average of 100 quintals (10 tonnes) of grapes, and consequently, more or less 70 hectoliters of finished wine can be obtained, which is 9,300 bottles of 0.75 cl.
The quantity of water available to the winemaker is not insignificant: hypothesizing a grape production of 80-130 q/ha, from which 56-100 q/ha are obtained, yielding 56-70 hl of wine per ha and 70 hl of wine per ha, and a water-effluent ratio equal to 1, approximately 6–7 m3 of wastewater will be available annually.
The activity of the oenological company is not limited only to the harvest period but, between "racking" and "bottling," it essentially extends throughout the year.
The terms of the problem, allowing for due exceptions related to site geography, seasonal climatic conditions, variety of "cultivars," and processing, can be summarized as follows:
- Approximately 13–15 tons of grapes are obtained from one hectare of vineyard.
- The processing of one ton of grapes generates, on average:
700 lt of wastewater
300 Kg of solid residues.
- 80% of the solid residues is destined for the distillery and consists of:
Pomace (approx. 200 Kg/tons)
Lees (approx. 50 Kg/tons)
- The remaining 20% consists of approximately 30 Kg/tons of processed grapes, made up of stalks and solid material (approx. 20 Kg/tons)
resulting from filtration and clarification.
Regarding the typology of the wastewater that is the object of our interest, these are characterized by a high organic load, due to Carbon linked to sugars and which is easily biodegradable, and partly to a residual component, linked to tannins and organic acids, which is less biodegradable.
Indicatively, the organic load, expressed as COD (Chemical Oxygen Demand), fluctuates between 500 mg/lt and 1,000 mg/lt in the period between November and March, rising to 1,000 mg/lt – 1,500 mg/lt from April to July, and then settling between 2,500 mg/lt and 3,000 mg/lt during the harvest period, between August and October; peaks of 8,000 mg/lt or more are not uncommon during this period.
Conversely, the effluent is poor in Nitrogen and Phosphorus, contents which often do not exceed 2 mg/lt; Phenols are around 1 mg/lt, while the range for surfactants is wider and can reach 5 mg/lt, depending on the ongoing processing.
The purification plant must be sized based on the daily flow rate of the effluent; to obtain a correct value of the water consumed and for greater precision in the sizing calculations, reference must be made to specific data collected directly in the cellar.
The verification between theoretical values and experimental data can be carried out, considering the production capacity of the oenological facility and the winemaking process itself; therefore, for simplicity of understanding, the sizing of the purification plant will be performed for a specific production of x quintals processed during the year.
It is self-evident that the produced effluent must undergo a preliminary fine screening to remove any residual skins and grape seeds, before being collected in an equalization tank which absorbs load peaks, ensures the most stable quality level possible, and at the same time carries out the sedimentation of any fossil flours carried into the stream by the effluent.
Features and Operating principle
Systems for Small Wineries
The Effluent Treatment Plants for Small Wineries are built using the purification step described below:
Phytoremediation is a natural process for purifying wastewater that utilizes the principle of self-purification typical of aquatic environments. In these biotopes, pollutants are naturally removed through physical, chemical, and biological processes, among which filtration, adsorption, assimilation by plant organisms, bacterial degradation, and antibiosis are most effective.
Phytoremediation treatments are secondary biological treatments that require an upstream primary sedimentation treatment such as an Imhoff Tank or Two/Three-Chamber Septic Tank, Grease/Saponin Trap, but they can also be used as a final polishing stage downstream of an Activated Sludge purification plant.
Phytoremediation plants are used to treat point-source and diffuse pollution sources, including surface runoff stormwater, domestic effluent, and agricultural and livestock effluent.
Phytoremediation systems are also used to treat landfill leachate, industrial effluent (paper mills, textile industries, food industries, and wineries).
Vertical Flow systems consist of basins waterproofed with plastic liners and filled with gravel and/or sand of appropriate particle size, where the following types of plants are put in place: Abelia Rupestris, Cistus, Cotoneaster Franchetii/Salicifolia, Eleagnus Ebbingei, Evonimus, Gynerium, Hebe, Hypericum, Lavandola Officinalis, Mahonia Aquilfolium, Nandina Domestica, Nerium Oleander, Rosmarinum Officinalis, Teucrium Fruticans.
Vertical Flow Phytoremediation plants have the advantage of being able to be installed even on surfaces without elevation differences (flat ground), as they are equipped with a lift pump. Vertical Flow Phytoremediation plants with a recirculation system allow the use of smaller surfaces per Population Equivalent.
Systems for Medium-Sized Wineries
The Effluent Treatment Plants for Medium-Sized Wineries are built by combining the purification steps listed below:
Primary Sedimentation Imhoff Tank
Upstream of the biological treatment, an IMHOFF type tank is included, in which the primary sedimentation is located in the upper compartment of the tank; this phase is necessary to retain all settleable suspended solid bodies to reduce the organic load entering the biological treatment. Another main function is to retain fine non-biodegradable solid bodies that would cause clogging of diffusers, pipes, etc., which could be retained by very fine screens, but which would require daily intervention by the management staff. In this way, intervention will be occasional, carried out by sewage vacuum truck.
Effluent Lifting/Accumulation
The effluents are collected in an adequately sized sump and lifted to the subsequent aeration phase using two submersible pumps (one operating and one standby). The pumps are of the submersible type electrically connected to level probes for automatic start-up. The equalization of flow rates determines, as a positive indirect effect, a partial homogenization of the concentrations of the different pollutants and a consistent homogenization of the pollutant loads. The sizing of the equalization tank is given by the sum of an adequate daily compensation volume, a minimum volume required for the continuous operation of the aeration/mixing equipment for the simultaneous execution of the purification processes, and any necessary volume for the equalization of discontinuous loads, considering an adequate safety margin.
Effluent Oxidation
This phase is sized so that the sludge loading factor towards the oxidation compartment is adequate. The volume of the tank, however, will be such as to ensure a suitable retention time, calculated based on the lifted flow rate. The aeration system is provided with side channel blowers, sufficient to supply the aerated mixture with the correct dissolved oxygen concentration. The air will be dispersed inside the tank by a series of tubular or disc porous diffusers, arranged along the longitudinal wall.
Final Sedimentation
The sedimentation tank is of the static type (DORTMUND). This phase is sized paying particular attention to the rising velocity and the retention time. The tank is complete with a peripheral stainless steel channel for collecting the purified water. The hopper walls have a slope greater than 45° to facilitate sludge collection. A submersible pump is used for lifting the secondary sludge to be sent to the Imhoff tank, which also ensures the continuous recirculation of sludge upstream of the biological treatment.
Phytoremediation
Phytoremediation is a natural purification system for domestic, agricultural, and sometimes industrial wastewater, which reproduces the principle of self-purification typical of aquatic environments and wetlands. This technology involves the purification of wastewater through the use of a waterproofed basin in which the gravel substrate and the vegetation combine their action to clean the water.
Untreated water flows in the bed of gravel and aquatic plants: here microorganisms come into play which, through biochemical reactions, eliminate pollutants.
The action of the plants is fundamental because the microorganisms necessary for the entire system develop in their roots: by absorbing the oxygen produced by the plant species, they trigger the chemical processes necessary for water purification.
Aquatic plants have the function of creating a suitable habitat for the growth of bacterial flora.
In practice, aquatic plants capture oxygen from the atmosphere and transport it from the leaves, through the stem, to the roots of the plant and then into the rhizosphere (the layer of earth where the plant's rhizomes are located), making it available to the aerobic bacteria present in the substrate.
These bacteria, which live in symbiosis with the plants, need oxygen to live and perform their function.
Their role is to degrade pollutants and organic substances, transforming them into inorganic substances available to the plants.
The plants in turn also contribute to purification because they absorb, as nutrients for their growth, a part of the substances dissolved in the water and transformed by the bacteria.
Anaerobic Digestion of Imhoff Tank Sludge
The activated sludge produced by the transformation of organic matter by specific bacteria, separated and collected at the bottom of the sedimentation hoppers, is continuously recycled to the aeration phase, while a part, the surplus consisting of the daily excess production, is periodically extracted and sent to the ANAEROBIC DIGESTION compartment of the IMHOFF type TANK; subsequently, the stabilized sludge will be disposed of according to law.
Systems for Large Wineries
The Effluent Treatment Plants for Large Wineries are built by combining the purification steps listed below:
Primary Sedimentation Imhoff Tank
The Imhoff tank is divided into two compartments, the upper compartment is called Primary Sedimentation. This phase is necessary to retain settleable solid bodies to reduce the organic load entering the subsequent biological treatment.
Effluent Lifting/Accumulation
The effluents are collected in an adequately sized sump and sent to the biological treatment using submersible pumps. The equalization of effluents produces, as an indirect effect, the homogenization of the characteristics of the different pollutants.
Biodisc Oxidation
The process is based on aerobic biological treatment with attached biomass, where the Biodisc is used as an inert support on which the bacterial flora develops.
This system is nothing more than the artificial application of the natural self-purification process (lakes, watercourses), with the difference that the bacteria in the unit (Biodisc Oxidation compartment) are found in higher concentration and in a reduced space.
The support alternately brings the flora itself into contact with the organic matter contained in the effluent to be treated and with atmospheric oxygen.
The microorganisms constituting the biological flora, placed in direct contact with the two determining elements for their development and activity, directly absorb the greatest possible quantity of organic matter during the immersion phase in the effluent and the proportionally necessary oxygen during the emergence phase.
Final Sedimentation
Final Sedimentation allows the separation of the purified water from the sludge; the water on the surface flows out towards the exit using a peripheral stainless steel channel with Thompson weirs, while the settled sludge is sent, via a submersible pump, to the head of the Imhoff tank as surplus sludge for disposal, following anaerobic digestion.
Secondary or biological sludge is different from primary sludge, which is separated from the raw effluent without undergoing any transformation by bacteria.
Phytoremediation
Phytoremediation of civil and industrial wastewater is a natural-based method for wastewater purification.
This system essentially consists of a basin whose side walls and bottom are waterproofed with suitable lining sheets.
The same basin has a superficial layer consisting of aquatic plants and is then entirely filled with gravel material, which is chosen with different particle sizes because its main function is to act as a filter for the wastewater that must then be purified.
The process of water purification occurs through the combination of a series of chemical actions that are created between the gravel, the plant varieties that are installed, and the microorganisms that develop within this context.
The main role is played by the plant organisms, whose primary task is to purify the wastewater collected within this basin, by absorbing the nutrients contained within them.
A Phytoremediation plant is capable of performing its function just a few months after start-up, particularly if the aquatic plants are installed in the spring.
The species of aquatic plants to be used vary according to the type of Phytoremediation plant to be built.
The system operates without added energy and therefore without electromechanical parts.
This allows the plant to be defined as "eco-compatible."
Phytoremediation plants, when appropriately sized, allow for a reduction of the organic load in the influent effluent exceeding 90% and in any case compliant with legal limits (Legislative Decree 152/06).
Anaerobic Digestion of Imhoff Tank Sludge
The produced sludge is conveyed under the hoppers of the Imhoff tank and periodically extracted from the Anaerobic Digestion compartment using tank trucks, to then be disposed of according to law.
Dimensioning
To discharge in compliance with the table limits, refer to the plant sizing required by Table 3, Annex 5 of Legislative Decree 152/06 for discharge into surface water.
To size the discharge Plants in compliance with the imposed table limits, please contact our Technical Office.