Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/20—Treatment of water, waste water, or sewage by degassing, i.e. liberation of dissolved gases
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/34—Treatment of water, waste water, or sewage with mechanical oscillations
  • C02F1/36—Treatment of water, waste water, or sewage with mechanical oscillations ultrasonic vibrations
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/16—Nitrogen compounds, e.g. ammonia
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/20—Nature of the water, waste water, sewage or sludge to be treated from animal husbandry

Definitions

• the present invention relates to a process for reducing the nitrogen content of zootechnic refluents .
• the present invention falls within the technical sector of treatment of zootechnic refluents containing animal dung deriving from livestock breeding of pigs, cows, chickens and other animals.
• national and international environmental regulations have imposed and impose increasingly restrictive limits to the quantity of nitrogen which can be distributed in the environment by the spreading of animal dung on farmland.
• the limits imposed on the spreading of dung in those farming areas where the concentration of nitrates in the ground have reached such high levels as to be defined "Nitrate Vulnerable Areas" are increasingly more restrictive .
• a medium-sized pig farm (3000-5000 animals) produces a quantity of such refluent varying from 30 to 50 m 3 /day.
• An almost total removal of the nitrogen (98-99%) may be obtained using refluent treatment processes of an organic type. These processes, which comprise at least a phase of organic oxidation of the refluent followed by a phase of denitrification are however v& ⁇ complicated to manage as well as requiring the installation of rather costly systems .
• a type of refluent treatment process enabling reduction of the nitrogen to acceptable levels and, at the same time, at a limited cost compared to the known state of the art processes, is one based on the stripping of the nitrogen contained in the refluent in the form of ammonia.
• This type of process typically performed in a plate tower or Raschig rings, foresees stripping of the ammoniacal nitrogen by means of insufflation of a current of air (stripping current) in counterflow to the descent of the liquid refluent with consequent removal of the gaseous ammonia.
• the refluent is generally heated and basifying agents are added, such as NaOH.
• the refluent must also be graded or filtered, if necessary after the addition of flocculants, since the presence of solids, even if of a small size, may obstruct the holes in the plates or dirty the Rashig rings, causing the system to block.
• the refluent must be heated to a temperature of over 8O 0 C with a very high energy consumption.
• the stripping current containing the gaseous ammonia is generally treated in scrubbers with acid solutions. Once the gaseous ammonia has been absorbed in the washing solution, the gaseous current free of nitrogen is released into the atmosphere.
• the purpose of the present invention is to identify a process for reducing the nitrogen content of zootechnic refluents which overcomes the drawbacks of the known technique and, specifically, which proves more viable both from an energetic and economic point of view.
• the object of the present invention is therefore a process for reducing the nitrogen content of zootechnic refluents comprising the following operative phases: [0015] a) placing the refluent in contact with a basifying agent in a reactor;
• phase b) c) recovering the ammonia from the outgoing gaseous current of phase b) with formation of a purified gaseous current .
• the process is conducted by using an ingoing gaseous current in phase b) composed of one or more gases and/or vapours chosen from: air, nitrogen, argon, carbon dioxide, helium, hydrogen, oxygen, water vapour and/or their mixtures .
• gases and/or vapours chosen from: air, nitrogen, argon, carbon dioxide, helium, hydrogen, oxygen, water vapour and/or their mixtures .
• the process according to the present invention applies to refluents coming from farms breeding various animals, such as pigs, cows, chickens etc and more generally to all refluents containing nitrogen in ammoniacal form, such as those remaining after anaerobic digestion treatment.
• the refluents collected from a single farm or from several farms are stored in a collection tank. They are generally in the form of a liquid-sludge such as to be agitated by means of the pump systems typically used in the sector. Sometimes, depending on the nature of the refluents and the characteristics of the farm producing them, before being subjected to treatment, the refluents may be mixed together and/or diluted with water so as to acquire sufficient fluidity to be agitated using the aforesaid pumping systems . [0021] The process according to the present invention is generally conducted in a single reactor which is filled with the refluents by means of pumping systems.
• the reactor is filled with the refluents in a fully automatic manner.
• Phase a) of the process according to the present invention preferably consists of placing the refluent, characterised by a neutral pH, in contact with a quantity of basifying agent able to raise the pH value up to a value varying from 7.2 to 13, preferably from 10.0 to 13.
• the basifying effect is preferably performed by a solid basifying agent chosen from CaO, MgO and/or their mixtures or chosen from watery solutions of Ca (OH) 2/ Mg (OH) 2 and/or their mixtures.
• the basifying agent is in a solid, granular form. Unlike the basifying agents used in the state of the art processes (e.g. NaOH) , these additives have a significantly lower cost .
• the preferred basifying agent is quicklime, that is a CaO/MgO mixture.
• the present invention may however be realised with the same additions, albeit in a limited form, with other basifying agents such as Na 2 O, K 2 O, NaOH, KOH, Na 2 CO 3 , K 2 CO 3 and/or their solid mixtures or with the respective watery solutions and/or their mixtures .
• the basifying agent may be added to the refluent to be treated in solid form or as a watery solution.
• its dosage varies from 5 to 20 kg of agent per m3 of refluent to be treated.
• the dosage When added in the form of a watery solution, typically at 30% in weight, the dosage varies from 30 to 50 litres/m 3 .
• the gaseous current introduced is composed of one or more gases and/or vapours chosen from the group comprising: air, CO 2 , N 2 , Ar, He, H 2 , O 2 , water vapour and/or their mixtures.
• air is used.
• the pressure of the gaseous flow generated to extract the ammonia is variable from -100 mbar (negative pressure reactor - aspirated gaseous current) to 100 mbar (gaseous current introduced) , in other words the gaseous flow which enables extraction of the gaseous current comprising ammonia may be generated either by introducing a gaseous current which runs over the free surface or by placing the reactor in negative pressure .
• the pressure of the gaseous flow is chosen from -10 to +10 mbar.
• the gaseous flow generated is present above the surface of the refluent without bubbling through it .
• the gaseous flow draws the ammonia which gradually separates from the refluent, outside the reactor.
• the gaseous current comprising the ammonia is then directed to the subsequent phase c) of the process.
• the gaseous flow generated over the refluent and especially on the free surface of the refluent inside the reactor, being produced by means of a gaseous current introduced in low pressure or by placing the reactor in slight negative pressure entails a modest consumption of energy.
• the process which the present invention relates to therefore enables the removal of the nitrogen from the refluent at favourable economic conditions compared to the state of the art stripping processes known of, which, use gaseous currents at significantly higher pressure.
• gas and/or vapour pumping systems of modest dimensions easily found for sale at a limited cost are sufficient .
• the refluent may be heated and kept at a temperature of about 50 0 C, for example, by means of special heating elements, such as coils immersed in the body of the refluent. At this temperature the formation of foam caused by the decomposition of the bicarbonates is avoided, as is the precipitation of the insoluble carbonates with consequent formation of calcareous incrustations on the walls of the reactor and on the heating coils. Heating may be particularly useful in the winter period when the refluents collected are at an average temperature of 15-20 0 C, while in the summer period the temperature of 40-50 0 C of the refluent is easy to reach.
• the extraction process of the nitrogen from the refluent according to the present invention proceeds at an acceptable speed even in the absence of agitation of the refluent.
• the gaseous ammonia in fact, evolves from the surface of the refluent by effect of the chemical action of the basifying agents and by the continual draw of the gaseous phase.
• the refluent may be kept agitated, for example, by mechanical means such as paddle mixers.
• the agitation of the refluent may be performed by insufflation into the body of refluent of at least a part of the gaseous current coming out of the reactor (non-purified current coming out of phase b) or from the gaseous current (purified current coming out of phase c) .
• agitation may also be obtained by the application of ultrasounds to the refluent.
• Agitation may also be obtained by the recirculation of a part of the refluent itself, taking it from the bottom of the reactor and re-introducing it in a second point of the reactor, situated above the free surface of the refluent, so as to create turbulence inside it.
• the recirculation capacity of the refluent varies from 0.2 to 3.5 recirculation cycles/hour, in other words such as to recirculate from 0.2 to 3.5 times in one hour the volume of refluent subject to treatment (e.g.
• the refluent in addition to the effect of the aforesaid recirculation, may be kept agitated by insufflation of air drawn from the outside.
• At least a part of the gaseous current coming out of the reactor may be used as gaseous current introduced in phase b) .
• all the gaseous current is purified and recycled in phase b) of the process so as to create a closed circuit of recovery.
• the refluent is discharged from the reactor and stored in tanks before being spread on farmland and/or used in part to pre-basify the new refluent to be treated. If the refluent is spread on farmland a correction of its pH may be needed so as to make it conform to the criteria established by environmental legislation on the matter.
• the end of treatment is determined automatically by means a system of continuous analysis which by continuously determining the concentration of nitrogen still present in the refluent (such as the ammonium ions) or extracted during the gaseous phase (such as gaseous ammonia) , is able to indicate the level of nitrogen reduction achieved by the process .
• the process according to the present invention described above is preferably performed in a batch mode, in other words, treating pre-defined quantities of refluent inside a single reactor until completion of the process. However, the process may also be performed in continuous mode by connecting two or more reactors in series .
• the gaseous current coming out of the first reactor, once purified of the ammonia, can be introduced into the subsequent reactor, increasing the speed of nitrogen removal from the refluent compared to the process conducted in a single reactor (with the same quantity of refluent treated) at the same time reducing the specific energy consumption of the process.
• the number of reactors and their size are chosen by a person skilled in the art so as to obtain an optimal "evaporation surface: volume of refluent" ratio, maximise the yield of ammonia extraction and minimise the energy costs and costs of chemical additives to be used, depending on the specific chemical composition of the refluent .
• the reactors may be made from plastic or composite material, stainless steel, rust-resistant steel alloy or waterproof concrete .
• the gaseous current coming from phase b) is made to pass over the free surface of an acid solution which captures the ammonia and neutralises it, forming the corresponding ammonium salt.
• an acid solution which captures the ammonia and neutralises it, forming the corresponding ammonium salt.
• watery solutions of an acid chosen from sulphuric acid (H 2 SO 4 ) , phosphoric acid (H 3 PO 4 ) , nitric acid (HNO 3 ) , carbonic acid (H 2 CO 3 ) and/or their mixtures.
• the ammonium salts solution may be effectively used as a fertiliser.
• concentration of ammonium salt varies (depending on the type of acid used) from 150 to 350 g/1 and the quantity of solution which can be obtained varies from 1500 to 2000 litres a day, implementing for example the process according to the present invention in a farm of 10,000 pigs .
• condensation systems e.g. condensation towers
• condensation systems e.g. condensation towers
• the current can be used as is or mixed with other combustibles.
• a fraction of such current is sent for combustion and the remaining fragment is used as a reagent to neutralise the nitrogen oxides (NOx) produced by the combustion of the first fraction.
• NOx nitrogen oxides
• a further alternative for the recovery of the ammonia extracted from the refluent is that of liquefaction. Compressing the gaseous current containing the ammonia, after dehydration and in appropriate temperature and pressure conditions, it is possible in fact to obtain the separation of the ammonia in liquid form.
• CaO or MgO and/or their solid mixtures may be used. Performing the process according to the present invention on a farm of 10,000 pigs for example, it is possible to obtain about 150 ⁇ 200 kg/day of liquid ammonia.
• a further advantage of the process according to the present invention is provided by the possibility of using the process by-product, that is the ammonia recovered in the form of ammonium salts in a watery solution, liquid ammonia or solution of ammonium hydroxide, as farm fertiliser or as a raw material for other industrial processes .
• FIG. 1 One possible form of enactment of the process according to the present invention is shown in the block diagram in figure 1, showing the various phases of the process as indicated below: [0074] (1) filling the reactor with the refluent to be treated;
• Example 1 [00101] 4000 litres of refluent coming from a pig farm and containing 4500 mg/l of nitrogen in ammoniacal form, (equal to 68% of the total nitrogen of the refluent) , corresponding to a total quantity of 18 kg of nitrogen in ammoniacal form were treated for 2.5 hours in a single reactor system. 40 kg of a mixture of CaO and MgO in granules were added to the refluent to bring the pH to a value of 11.2. The pressure of the gaseous current introduced was 5 mbar and the flow rate was 4000 Nmc/h. [00102] The flow rate of recirculation of the refluent was set at 800 litres/hour.
• the gaseous current containing the ammonia coming out of the reactor was made to flow on the free surface of a solution (having a volume of 500 litres) of H2SO4 at 9.14% in weight.
• concentration of the ammonium in the refluent was approx. 300 mg/l; this means that 4200 mg/l of ammonium were extracted from the refluent, giving rise to 500 litres of solution at 12.5% in weight of ammonium sulphate .
• Example 2 [00105] 8000 litres of refluent coming from pig farms and containing 3000 mg/l of nitrogen in ammoniacal form,
• the flow rate of recirculation of the refluent was set at 2000 litres/hour.
• the gaseous current containing the ammonia coming out of the reactor was washed in a scrubber with an acid solution for sulphuric acid at 20% (volume of the washing tank of the scrubber 1000 litres) .
• the final concentration of the ammonium ions in the refluent was approx. 500 mg/1, corresponding to an extraction of 20kg in all of ammonium which produced 74kg of ammonium sulphate in acid solution.
• the final concentration of sulphuric acid in the washing tank, after treatment of the refluent was 14.6% in weight.
• a process to reduce the nitrogen content of a zootechnic refluent comprising the following operative phases: [00113] a) placing the refluent in contact with a basifying agent in a reactor in such a quantity as to bring the pH to a value varying from 7.2 to 13; [00114] b) keeping the refluent deriving from phase a) agitated; [00115] c) recovering the ammonia from the gaseous current which is generated in phase b) ; wherein [00116] - the refluent is kept agitated in phase b) by insufflating all or a part of the gaseous current purified or not of the ammonia deriving from phase c) ; and/or
• phase a) of the process consists of placing the refluent, generally pH neutral, in contact with a quantity of basifying agent able to raise the pH value to a figure varying from 7.2 to 13 and preferably from 10.0 a 13.
• phase b) of the process according to the present variation the refluent is kept in constant agitation so as to support the aforesaid process, facilitating stripping of the gaseous ammonia.
• all the gaseous current, purified or not is recycled at phase b) of the process according to the present variation, so as to create a closed circuit of recovery.
• a part of the refluent being treated is extracted from a point situated in the lower part of the reactor by means of pumping and re- introduced in another point situated in the upper part of the reactor, above the free surface of the refluent, so as to create further turbulence and encourage stripping of the ammonia.
• the flow rate of recirculation of the refluent varies from 0.2 to 3.5 recirculation cycles/hour, in other words such as to recirculate from 0.2 to 3.5 times in one hour the volume of refluent subject to treatment (e.g. if the volume of refluent to be treated is 5000 litres, 2 circulation cycles/hour correspond to a recirculated volume of 10,000 litres/hour) .
• the agitation in phase b) may be made even more efficient by using, in addition to the recirculation of the air, purified or not, and of the refluent treated, mechanical means of agitation and/or mixing (e.g. paddle mixer) .
• the refluent in addition to the effect of the aforesaid recirculation, may also be kept agitated by insufflation of the air captured from outside.
• One preferred form of enactment of the process according to the present variation is shown in the block diagram in figure 3, showing the various phases of the process as indicated here: [00125] (1) filling the reactor with the refluent to be treated;
• phase (A-I) and (A-2) may entail the phases :
• the stripping current containing the ammonia was made to bubble through 200 litres of a watery solution at 15% in weight of H2SO4 and 14% in weight of HN03. [00142] At the end of treatment the complete removal of the ammoniacal nitrogen of the refluent was achieved and 200 litres of solution of ammonium salt composed of 36.9% in weight of ammonium sulphate and 18.2% in weight of ammonium nitrate utilisable as agricultural fertiliser was produced .

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Cited By (5)

Citations (3)

• 2007
  • 2007-12-31 IT ITMI20072448 patent/ITMI20072448A1/it unknown
• 2008
  • 2008-12-04 WO PCT/IB2008/055105 patent/WO2009087507A1/en active Application Filing

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