Process for utilizing liquid manure material

Details Process for utilizing liquid manure material Process for utilizing liquid manure material

1999-07-06

2002-05-14

Griffin, Steven P. (Department: 1754)

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

C071S015000, C071S033000, C210S638000, C210S651000, C210S655000, C210S697000, C210S724000, C210S767000, C210S903000

Reexamination Certificate

active

06387272

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for utilizing the material of ammonium-containing effluents in, for example, liquid manure.
Liquid manure arising in agricultural livestock production exhibits a high content of nitrogen, phosphorus and potassium. It has a considerable nutrient potential and is therefore useful as a fertilizer. However, directly applying liquid manure to agriculturally productive land, such as is presently practiced, creates risks to the environment. Thus, climate-damaging methane gas is released by the liquid manure. By nitrification of ammonia, the liquid manure constituent, nitrate is formed which pollutes water courses. The use of liquid manure, on a large scale, can easily cause overfertilization, and the nitrate content of the groundwater can exceed the recommended limits. Ammonia passes into the atmosphere and is transported back to the ground, for example, with rain over forested areas. The associated introduction of nitrogen represents an undesired additional fertilization which can contribute to an overfertilization of the forests.
As an alternative to the disposal of liquid manure by its use in fertilization of agriculturally productive land, environmentally friendly processing of the liquid manure with recovery of the valuable materials contained therein is currently desired. One valuable material contained in the liquid manure is ammonia. Depending on the pH, ammonia is present as physically dissolved ammonia or in the form of ammonium ions. The processes for the removal of ammonium from ammonium-containing effluents that are presently practiced operate by precipitation of ammonium in the form of magnesium ammonium phosphate. The precipitated salt obtained, magnesium ammonium phosphate, represents a valuable material. This can, for example, be used as a fertilizer or decomposed, for the recovery of ammonia, to give ammonia and magnesium hydrogen phosphate.
2. Description of the Related Art
DE-A 3,732,896 discloses a process for eliminating ammonium and phosphate from an effluent. By addition of magnesium salt and/or magnesium oxide, ammonium and phosphate are crystallized out and separated off as MgNH
4
PO
4
PO
4
.6H
2
O (magnesium ammonium phosphate). If appropriate, after previously separating off solids, the process can be used for domestic and industrial effluents and also special effluents having a high ammonium content, for example, liquid manure.
DE-A 4,040,067 describes a process for the recovery of the ammonium content from process waters and effluents employing precipitation of magnesium ammonium phosphate, wherein, for accelerated precipitation and separation of magnesium ammonium phosphate, magnesium hydrogen phosphate and caustic soda solution are simultaneously added in a precipitation stage to the effluent to be treated. The separated magnesium ammonium phosphate is thermally split into ammonia and magnesium hydrogen phosphate in a regeneration stage, the precipitant being recovered and recycled into the precipitation stage.
A disadvantage of the known processes is that, because of the comparatively small ammonium concentrations in the treated effluents, relatively large liquid streams must be moved during precipitation and the subsequent separation of the precipitated salt. The ammonium-free effluents recovered also contain further undesired soluble constituents which partly originate from the precipitant used. For removing these, large quantities of liquid must again be processed. This results in processes which are economically prohibitive, for example, for processing liquid manure in a continuously operating installation.
SUMMARY OF THE INVENTION
It is one object of the invention to provide a process for environmentally friendly processing and utilization of liquid manure material. The ammonium contained in the liquid manure is recovered by separating the ammonium off as a valuable material in the form of a precipitated salt. The process permits the quantity of liquid to be processed to be greatly reduced and therefore operates more economically.
These objects are achieved by a process for recovering ammonium from ammonium-containing effluent which contains additional soluble constituents and, optionally solids if present, comprising:
a) optionally, separating off the solids,
b) concentrating substantially solids-free ammonium-containing effluent to give an aqueous concentrate having an increased content of ammonium and additional soluble constituents, with simultaneous recovery of substantially ammonium-free pure water,
c) precipitating ammonium as magnesium ammonium phosphate in the ammonium-containing aqueous concentrate, and
d) separating off precipitated magnesium ammonium phosphate with recovery of substantially ammonium-free residual concentrate which at least partially contains the further soluble constituents.
Further objects, features and advantages of the present invention will become apparent from the detailed description of preferred embodiments that follows.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The term “ammonium” as used below is a general term for physically dissolved ammonia and ammonia in the form of ammonium ion, unless differentiation between the two species is explicitly made. Ammonium-containing effluents include but are not limited to domestic and industrial effluents and also special effluents, such as water seeping from landfills, coke oven water, manure or liquid manure having an increased ammonium content. In addition to ammonium, the effluents mentioned contain additional soluble constituents, for example, those which pollute water courses. Examples include soluble constituent cations, such as, Na
+
, K
+
, Mg
+
, Ca
+
, Fe
2+
, Cu
2+
, Zn
2+
and anions such as chloride, nitrite, nitrate, sulphate, carbonate and phosphate.
According to the invention, the effluents mentioned can be concentrated before precipitation of ammonium is carried out. An aqueous concentrate having an increased content of ammonium, and possibly additional soluble constituents, and a purified substantially ammonium-free effluent (pure water) are obtained. The substantially ammonium-free pure water can still have a residual ammonium content of <250 mg/l, preferably <100 mg/l, particularly preferably <50 mg/l. The substantially ammonium-free pure water may contain at least a part of the possible additional soluble constituents, preferably at a markedly reduced extent. Preferably, the content of additional soluble constituents is so small that the pure water can be released into the outflow of an effluent treatment plant. The content of additional soluble constituents can include chloride ions generally present in an amount <50 mg/l, preferably <100 mg/l, and particularly preferably <50 mg/l; potassium ions generally present in an amount <200 mg/l, preferably <150 mg/l and particularly preferably <100 mg/l; sodium ions generally present in an amount <100 mg/l, preferably <50 mg/l, and particularly preferably <20 mg/l; copper ions generally present in an amount <1 mg/l, preferably <0.3 mg/l and particularly preferably <0.1 mg/l; magnesium ions generally present in an amount <1 mg/l, preferably <0.5 mg/l, and particularly preferably <0.2 mg/l; COD (chemical oxygen demand) generally present in an amount <1000 mg/l, preferably <500 mg/l and particularly preferably <200 mg/l;
During the concentrating step of the ammonium-containing effluent, precipitation can be carried out with a substantially reduced quantity of liquid. Moreover, the pure water is obtained already before precipitation is carried out. In this way, it is possible to avoid additional increases in the salt content, which may be caused by the over-stoichiometric addition of precipitant to the ammonium-containing effluent during the precipitation step.
Preferably, the concentrating of the ammonium-containing effluent can be carried out by reverse osmosis. The concentrating factor then amounts in general to between

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