Environmental Technology, Vol. 22. pp 1313-1324
© Selper Ltd, 2001
REM NUT ION EXCHANGE PLUS STRUVITE
PRECIPITATION PROCESS
L. LIBERTI*, D. PETRUZZELLI AND L. DE FLORIO
Department of Civil and Environmental Engineering, Polytechnic University of Bari
V.le Turismo 8, 74100 Taranto, Italy
(Received 15 March 2001; Accepted 4 June 2001)
ABSTRACT
Nutrients control technologies from wastewater are based on destructive technologies which defer the problem from the
diluted liquid-phase (effluent) to a more concentrated waste (sludge) in the case of phosphates, or to nitrogen gas and/or
volatile compounds in the case of ammonia. The REM NUT process allows for simultaneous removal of phosphate and
ammonium ions by selective ion exchange and recovery by chemical precipitation in the form of struvite (magnesium
ammonium phosphate) from the spent exchangers regeneration eluates. In the paper revised versions of the REM NUT
process, i.e., P-driven layouts, are presented and cost effectiveness is compared to chemical precipitation based on the use of
ferric chloride.
Keywords:
Wastewater P-removal; P-recovery; magnesium ammonium phosphate; struvite
fertiliser manufacture [3].
Conventional Methods for P Removal at Municipal and
Industrial WWTP are based on:
INTRODUCTION
The west European phosphate industry has fixed an
objective of using 25% recovered phosphates (probably the
only recyclable detergent ingredient) within a decade and has
recognised sewage and animal wastes among the major
alternative sources of P [1]. Total P content of the above
waste streams amounts to approx. 5x105 and 8x105 t y-1
respectively [2].
A stricter regulatory pressure on P discharge to control
eutrophication, known limitations of biological P removal and
controls on the disposal of related P-laden sludge land are
triggering renovated interest toward alternative processes
with improved performance allowing for simultaneous
removal and recovery of nutrient species.
Current practice for industrial recycling of phosphorus
from waste water treatment plants (WWTP) is based on
phosphate precipitation as either calcium phosphates or
struvite (MgNH4PO4 and MgKPO4) pellets. The chemistry of
the two compounds is different, but integration of their
recovery into sewage treatment is similar. Calcium phosphate
may be recycled into industrial processes or processed to local
manufacture of fertilisers while struvite can probably be used
directly as fertiliser (although a better substantiation of its
economic value is needed) or it can be incorporated into

Chemical precipitation: FeCl3, Al2(SO4)3 , (AlCl3)n , Ca(OH)2
or their combination is added at various points in
WWTP inducing precipitation of insoluble phosphates,
removed as waste sludge and usually disposed-of in
sanitary landfills. The economic value associated with Pladen slurry is limited while sludge production increases
significantly [4,5].

Enhanced Biological Nutrient Removal (EBNR): provision
for an anaerobic zone in the activated sludge bioreactor
may allow for simultaneous removal of P (beyond the
need for biomass synthesis as "luxury uptake") and N
(through de/nitrification). P ends up in sewage sludge
(it may be incidentally recovered from supernatant
liquor after anaerobic digestion of sludge) while N is
stripped out to the atmosphere as nitrogen gas [4,6-8].
The European Directive No.271/91 on Urban
Wastewater [9], now enforced in all member States [10], sets
strict nutrient discharge limits to prevent eutrophication in
sensitive areas (1-2 mgP L-1), with a similar approach assessed
since the late seventies in the US and Canada Great Lakes area
1313
[11]. In addition to chemical precipitation, largely adopted
although relatively expensive, bio-P removal techniques have
attracted renewed interest on the international scene recently
although generally they are less technically effective to cope
with the Directive’s limits [7,12-16]. This is a consequence of
the (expected) lower operation costs of EBNR processes and
possible P recovery from sludge digestion supernatant. On
the other hand, chemical precipitation often yields excessive
sludge P content for spreading on agricultural land [17]. BioP removal, on the contrary, invariably induces P release by
hydrolysis during sludge digestion and this in turn may lead
to uncontrolled phosphate scaling in the form of struvite
(more often in anaerobic respect to aerobic sections) and
resulting malfunctioning may be so extensive to yield WWTP
shut-downs [18]
Over the last few years, resurgent interest has been
observed in the industrial recovery and recycling of
phosphorus. Several water companies have built or tested Precovery systems [13-16] and others are currently doing so on
full scale plants [19-24]. Among others the Crystalactor®
process, developed by DHV Water BV, The Netherlands
[19,20] and the Phosnix® process, developed by Unitika Ltd,
Japan [21,23,24], deserve special mention.
The REM NUT process presented in this paper,
developed at Italy’s National Research Council [25,26], allows
for P, NH4 and K removal from dilute streams through
selective ion exchange followed by struvite precipitation in
proper conditions. The process is suitable for different
applications, thus overcoming limitations of biological
processes, and may be integrated with
(rather than
substituted for) other P-recovery technologies, particularly as
a mainstream (tertiary) treatment in small-medium size
WWTP where bio-P might not be easy to operate.
THE REM NUT PROCESS
Developed in the mid 1980s for removal and recovery
of phosphate, ammonium and potassium ions from
wastewater in the form of a premium quality slow-release
fertiliser, i.e., ammonium and potassium struvite MgNH4PO4,
and MgKPO4 in its basic configuration the REM NUT process
relies on two unit operations (Figure 1):


selective ion exchange for removal of nutrients (NH4+,
K+, HPO4=) from wastewater and their concentration in
the ion exchangers’ regeneration eluate
chemical precipitation of nutrients from this latter in the
form of struvite after addition of Mg2+ at controlled pH,
while the supernatant solution is recycled.
The Main Features of the Process are:

1314
two ion exchange units, cationic and anionic, based on a
natural zeolite (Clinoptilolite, Phillipsite or Chabasite)
and a “scavenger” strong base resin respectively, are
used for selective removal (>90%) of nutrients from
wastewater to the discharge limits imposed by current
legislation according to:
Figure 1.
Conceptual scheme of the REM NUT process.
Z-Na + NH4+ (K+) === Z-NH4 (K+) + Na+
(i)
Mg2+ + NH4+ (K+)+ HPO4= === MgNH4(K+)PO4 (s) + H+ (iii)
2R-Cl + HPO4=
=== R2-HPO4 + 2Cl-
(ii)
(Z = zeolite, R = anion exchanger)


regeneration of both ion exchangers is carried-out with
neutral 0.6M NaCl brine (i.e., seawater wherever
possible) with cyclic regeneration make-up as low as 2BV
(ion exchanger Bed Volume) through a “zero discharge”
closed loop technique [27]
cation and anion exchangers’ regeneration eluates are
properly mixed, pH is raised to 9.5 (where incidental
presence of heavy metals retained by the zeolite is
precipitated) and a soluble Mg salt (e.g., MgCl2) is added
to yield a virtually non-toxic sterile struvite-rich
precipitate (Table 1) according to:
Table 1.
Overall effluent quality is improved by additional side
benefits including incidental removal of residual suspended
solids (90%), biological oxygen demand, chemical oxygen
demand, (i.e., bio-persistent refractory organics, phenol
derivatives, surfactants, pesticides, endocrine disrupters,
oestrogens etc., >65%) and microorganisms (90%). Reduction
of these latter (approx. 1 log) in particular will proportionally
minimise disinfection demand and related health hazards
associated with haloforms formation (THM, AOX) during
final chlorination.
The process passed extensive laboratory study [28],
pilot scale investigation [29] and two demonstration
campaigns with a fully automated 240 m3d-1 pilot plant
(Figure 2) carried out at West Bari, Italy, WWTP (MayDecember 1983, funded and supervised by Italy’s National
Research Council) [30,31] and at South Lyon, MI, USA,
WWTP (January-May 1986, funded and supervised by the
U.S. Environmental Protection Agency) [32,33].
Typical analysis of struvite-rich precipitate recovered from municipal sewage with REM NUT process.
Struvite content : >93% w
Organic matter: <7% w
MgO:P2O5:N=15:27:5
As<0.3; Cd<0.5; Cr(VI)<0.1; Crtotal<0.35; Cu<0.2; Hg<0.5; Pb<4.5; Se<0.02
Ni<2; Zn<25; Fe<200 (mgkg-1)
Microbial charge: almost sterile
Radioactive content: nil
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Figure 2.
Outside view of 240 m3 d-1 REM NUT mobile plant.
In spite the of promising results achieved, however, the
organic phase (activated sludge) and the effluent supernatant
REM NUT process did not reach full scale application yet due
is admitted to the P-driven REM NUT scheme. The NH4essentially to:
loaded zeolite may be conveyed to bio-regeneration through

unbalance between P and N in municipal sewage (P:N 
nitrification-(de)nitrification and then recycled.
1:10 on molar basis), and hence in the exchanger
In all cases approx. 1:1 stoichiometric amounts of P-PO4
regeneration eluates calling for the expensive addition of
and N-NH4 will be retained by selective ion exchange and
chemicals to yield P:N:Mg = 1:1:1 stoichiometry for
precipitated as struvite, after Mg addition to ion exchangers’
struvite precipitation
regeneration eluate. As mentioned, the final effluent is still

high P-discharge limits enforced in several EU Countries
acceptable for eutrophication control with improved quality
(e.g., 10 to 20 mg l-1 P in Italy)
in terms of COD, suspended solids etc.

poor attitude of (waste)water industry toward
With respect to the full version, the P-driven REM NUT
innovation
scheme obviously requires proper design and sizing of ion

relative abundance of the natural P deposits
exchange sections. Under these conditions cost-effectiveness
of process chemistry may largely improve as the external
The turn of millennium now offers a different scenario
addition of phosphatess to reach Mg:NH4:PO41:1:1 molar
for the last three drawbacks and promotes resurgent interest
ratio for struvite precipitation, is no longer required and
toward the REM NUT process, provided the P/N unbalance
chemical consumption is limited to Mg (MgCl2) and alkaline
could be addressed as discussed later.
buffer (NaOH) for pH control.
Additional savings of chemicals (80%) have been
estimated
with seashore installations where seawater may be
P-DRIVEN REM NUT SCHEME
used as ion exchangers regenerant and a source of Mg for
The REM NUT process was revisited for removing and
struvite precipitation as indicated by preliminary tests [35]
recovering all phosphate and just an equimolar amount of
and confirmed recently in Japan [24]. Through proper design
ammonium ion from sewage by selective ion exchange,
and arrangement of the basic flow-sheet other revisited REM
leaving excess NH4+ to other conventional treatment processes
NUT schemes may be assumed.
Among others, pre(e.g., bio(de)nitrification).
concentration of phosphate ion by selective anion exchange
The so-called P-driven REM NUT process may assume
followed by recovery as Ca-phosphate or struvite from the ion
different layouts as shown in Figure 3.
exchanger eluate was successfully tested on a demonstration
According to scheme 3a (full REM NUT), applicable
scale with animal wastes (pig farm) in Northern Italy [35].
with N:P1:1 molar ratio and nutrient-rich effluents (e.g.,
A pilot investigation is now planned to assess feasibility
animal wastes), the influent stream is processed on both ion
of the P-driven REM NUT scheme.
exchange units for quantitative recovery of phosphate and
ammonium load.
Scheme 3b (P-driven REM NUT) is
ECONOMIC EVALUATION
applicable with an unbalanced N/P ratio as, most commonly,
in municipal effluent (N/P 10/1). In this case, while the
Three process schemes (Figure 4) have been compared
whole stream is processed for PO4-selective ion exchange on
under design data and unit costs summarised in Table 2 for a
the anionic section, approximately 1/10 of the influent stream
typical 11,000 m3d-1 municipal installation discharging into
(i.e., a reverse fraction with respect to N/P ratio) undergoes
"sensitive areas" (i.e.,  1mg l-1 P final concentration).
NH4-selective ion exchange on the cationic unit and 9/10 is
Scheme A, based on the most common chemical postby-passed to other de-ammoniation treatment. Biological
precipitation of phosphorus by direct addition of FeCl3 and
nitrification-denitrification (bio N-deN) appears particularly
cationic polyelectrolyte to secondary effluent, was assumed as
suitable to this aim and offers great synergy. Indeed bio Nreference. Alternatively, the modified REM NUT layout was
deN will provide sidestreams or pints in the mainstream with
considered under two different schemes (B and C), both
relatively high NH4+ content (many bio N-deN works
typically including phosphorus pre-concentration by selective
“accidentally” achieve also some bio-P removal, but generally
ion exchange followed by chemical precipitation. Scheme B
not enough to cope with Directive P limits). The combination
refers to wastewater containing only phosphate ion (e.g.,
of bio N-deN (<90%) with P-driven REM NUT treatment will
nitrified sewage), to be more efficiently precipitated as ferric
offer a key configuration as water companies usually will not
phosphate from the P-concentrated anion exchanger
wish to address P removal independently from N removal
regeneration eluate. Scheme C applies to the wider case of
questions.
effluents containing both ammonia and phosphates (e.g., non
In another REM NUT scheme currently investigated
nitrified municipal sewage), to be recovered in a 1:1 molar
[34], excess ammonium is absorbed by Na-form zeolite added
ratio through selective ion exchange followed by struvite
directly into the WWTP activated sludge reactor. The mixed
precipitation with the so-called P-driven REM NUT layout.
liquor is then submitted to fractional sedimentation to
Almost the same amount of ferric phosphate (i.e.,
separate the mineral phase (ammonia-loaded zeolite) from the
176 t y-1) is recovered directly from diluted secondary effluent
1316
(10 mg l-1 P) in scheme A and from the concentrated
Figure 3.
ion exchange eluate (450 mg l-1 P) in scheme B. This latter, in
Schematic layouts of REM NUT process (Z-Na: sodium-form zeolite; R-Cl chloride-form resin).
spite of additional investment and operation, provides two
main advantages over scheme A:


a smaller precipitation reactor may be used with a more
concentrated phosphate solution
leakage of phosphate crystal fines in the final effluent
1317
(potentially exceeding P discharge limit) is prevented
through the recycling of precipitation supernatant.
An additional major advantage associated with scheme
C is the recovery of more valuable struvite (285 t y-1)
instead of ferric phosphate.
The resulting cost summaries for schemes A, B and C
are reported in Table 3 and compared in Figure 5. From the
above data, the finite convenience of the P-driven REM NUT
Figure 4. Flowsheet of P removal processes under comparison (flowrate; 11,000m 3d-1)A: Chemical precipitation. B: Chemical
precipitation following ion exchange. C: Chemical precipitation following P-driven REM NUT. (Z-Na; sodium-form
zeolite; R-Cl: chloride-form anion resin.
1318
Table 2.
Design data for P-removal from municipal sewage (mg l-1) and unit cost of chemicals (¤t-1).
Parameter
Influent
Effluent
Chemical
Precipitation
P-driven REM NUT
1
40-45
10-20
10-15
1
5
10
5-10
Product
Cost
Revenue
Ferric chloride
Cationic polyelectrolyte (°)
NaCl
MgCl2.6H2O
Sodium hydroxide
Struvite
250
3,370
200
500
650
P-PO4
N-NH3
BOD
SS
Flow-rate
10
50
25
80
11,000 m3d-1
500
(°) type Nymco Dryfloc 652
process is demonstrated. Relevant to this aim is the economic
revenue associated with recovery of struvite. The suggested
price of recovered struvite has varied between 500 ¤t-1 USEPA
[32,33] and 300 ¤t-1 [23,26] whilst recently the retail price on
the small market was set at 1,000 ¤t-1 [24]. Assuming an
intermediate figure of 500 ¤t-1, revenues would cover >40% of
O&M costs for scheme C (struvite) compared to as low as <3%
using Al or Ca precipitating agents. It has been assumed that
the market value of Fe-phosphate will at very best cover
transport and disposal costs and so it has been assumed to be
zero.
Although appropriate at this stage, no economic value
was associated with improved effluent quality after REM
NUT treatment and nutrients discharge control (related to
environmental sensitivity of areas of reference), was assumed
equivalent for all schemes under comparison.
Moreover, difference in transport costs of recovered byproducts was disregarded on the assumption that they could
be easily sold to local farmers or markets near WWTP
catchement areas (although reuse of Al or Ca phosphate
would unrealistically require a fertiliser factory next door).
FERTILISER VALUE OF STRUVITE
Magnesium ammonium phosphate is a relatively rare
mineral with the most important natural source being rotting
organic material such as guano (birds excrements) and animal
manure [37,38]. In addition to spontaneous precipitation from
biological digestion of municipal and animal sludge, it is a
common constituent of renal and vesical calculii in humans
and animals [39].
Magnesium (and potassium) ammonium phosphates
are the most important representatives of a group of
compounds
with
general
formula
MeNH4(K)PO4
(Me=divalent metal) wherein the elements may be necessary
for plant nutrition [37,38,40].
These compounds exhibit slight solubility in water
suggesting that they might be suitable as slow release nonburning fertilisers [38,40,41]. The rate of release to plants,
however, is often determined by bacterial action rather than
solubility, although evidence exists of the strong influence
exerted by granule sizes [42].
Laboratory studies on
pulverised struvite confirm that release rates are much greater
than expected on the basis of its solubility and it was
concluded that soil nitrification is the rate controlling factor in
nutrient release to plants [41,43]. Accordingly, fertiliser
granulation and dose play a relevant role in determining its
agronomic properties.
Stable forms of magnesium ammonium phosphate are
hexahydrate and monohydrate (transition temperature 57°C),
this latter being slightly less soluble in water (0.14 vs. 0.18 g l-1
at 25°C) [37,38].
Synthetic magnesium ammonium phosphate was
commercialised in the USA on a small scale essentially in the
monohydrate form (8%N, 40%P2O5, 25% MgO) and also as a
mixture of ammonium and potassium derivative to reach NP-K ratio exceeding 7-40-6 [37,38,44].
Several comparative studies with urea formaldehyde,
ammonium nitrate and ammonium sulphate to test nitrogen
release were carried out with success on ryegrass, bluegrass,
buckwheat, cicer arietinum and others [43]. As for phosphorus
response, struvite responded better (even double) than
1319
superphosphates and its effectiveness as a source of
magnesium which is completely soluble and ready available
to plants for nutrition was also demonstrated [43].
Many applications of struvite in the USA refer to
container grown ornamentals (pot flowers) [45], field grown
ornamentals [46] and plant nurseries, a market able to afford
the somewhat higher price of synthetic magnesium
ammonium phosphate thanks to the excellent results achieved
so far.
Struvite was successfully used to grow
chrysanthemums, poinsettias, azaleas and others [47]. Bushes
and trees also showed superior height and trunk diameter
[37,47,48,49,50].
In minor cases, a number of field crops (beets, winter
wheat, potatoes, tobacco) were fertilised with magnesium
ammonium phosphate with results comparable or even
superior to super-phosphates [47,51].
Tomatoes responded well to struvite application in
large field experiments in Florida where it gave greater yields
than other conventional fertilisers [37].
Magnesium potassium phosphate was used for limited
field crops in different experiments on ryegrass, bushbeans
and tomato under non-leaching conditions [49]. It resulted in
a good source of P and K, while under leaching conditions
potassium struvite showed finite superiority due to its lower
solubility with respect to closer equivalents (potassium
superphosphate and sulphate) [41,47].
ION EXCHANGE INDUSTRY
Ion exchange (IE) is a well established industrial
technology. Despite strong competition of membrane
technology
(reverse
osmosis,
nanofiltration
and
electrodialysis), IE continues to play an important role in
water treatment with specific reference to the power industry
(condensate polishing), the electronic industry (ultrapure
water >20 Mcm-1) and water conditioning generally in
different industry sectors [52].
More than 50% of world IE application refers to natural
water conditioning (i.e., softening, de-alkalization, demineralization, organic matter and colour removal, iron,
manganese and nitrate removal as well as specific
environmental applications with reference to heavy metals
removal).
Due to a smaller market demand beyond catalytic and
molecular sieve applications, commercial availability of
synthetic and natural zeolites is less developed than synthetic
resins, limited essentially to specialised applications in the UK
and USA.
1320
Figure 5. Overall economic comparison among three schemes proposed for P recovery from municipal sewage.
Table 3.
Cost summary for a 11,000 m3d-1 P removal and recovery plants based on the three proposed schemes (see Figure 4).
Capital cost (¤ x 103)
A
B
C
c1 precipitation reactor
175
20
20
c2 ion exchange columns
-
90
100
c3 resin inventory (*)
-
120
144
c4 pumps
20
13
15
c5 vessels
15
10
17
c6 bag filtration unit
15
10
7
c7 electric plant
8
10
13
c8 piping and valves
(10% c1-c7)
22.3
27.5
31.6
c9 installation
(5% c1-c8)
12.3
15
17.4
c10 instrumentation
(5% c1-c8)
12.3
15
17.4
c11 mounting and fittings
(5% c1-c8)
12.3
15
17.4
c12 engineering
(10% c1-c11)
28.2
34.5
40
310.0
380
440
(10 y, 5% y)
40
49.2
60
power
(0.1 ¤kWh-1)
5.3
17.5
18
labour
(1unit x 2shifts)
60
60
60
resin back-up
(5% y c3)
-
6
7.2
c15 maintenance
(5% c1-c11)
14.2
19
20
213
258.7
336.9
Total investment
Running cost (¤y-1 x 103)
c13 amortisation
c14 operation:
chemicals (°)
Total O&M cost
Revenue (¤y-1 x 103)
struvite
142.6
Net cost
213
258.7
194.3
Net unit cost (¤m-3)
0.053
0.064
0.048
(*) type Amberlite IRA 458 from Rohm&Haas Co.,USA (schemes B and C)
type Zeolyst 13x18x80 from PQ Corporation,USA (scheme C)
(°) FeCl3, PE (scheme A); NaCl, FeCl3 (scheme B); NaCl, MgCl2, NaOH (scheme C)
Worldwide sales of ion exchange resins exceed 300 M¤
y-1 [52]. With an average unit cost for synthetic resins
between 2,000 to 4,000 ¤ t-1 and assuming 10% annum for
resins inventory, the associated business may be easily
quantified.
c)
The Main Negative Features of IE Technology are:
a)
b)
Relatively high cost (particularly with chemicals for
resins regeneration) hardly acceptable for municipal
wastewater treatment
environmental impact related to disposal of resin
regeneration eluates
1321
easy fouling of ion exchangers.
The above limitations may be minimised through a "zero
discharge" approach relying on maximum resin
regeneration efficiency like the “closed loop” technique
developed for the REM NUT process. This latter uses a
“scavenger” strong base anion exchanger1, selected after
extensive kinetic and thermodynamic investigation of
the phosphate/sulphate/chloride multi-anion system
extended to over 50 commercial anion exchangers. The
updated version of this product is regularly marketed at
average price (4,000 ¤ t-1) and exhibits improved kinetic
behaviour and enhanced resistance to fouling.
A novel ion exchanger with improved P-selectivity has
been proposed quite recently [53] and contacts are in progress
to evaluate applicability to the REM NUT process.
As for the cation exchanger a clinoptilolite equivalent
synthetic zeolite2 or a natural Phillipsite with improved
selectivity toward NH4 ion have been identified, also
exhibiting improved kinetic and thermodynamic performance
[34]. These were preferred to the natural Clinoptilolite3 used
in previous applications of the REM NUT process that, given
the geographic localisation of extraction sites (Eastern Europe,
Russia, USA), might be subject to market unavailability.
It is hoped that development of the P-driven REM NUT
process will potentially shed new business opportunities on
the IE market, with reference to either the above mentioned
products or to equivalent materials. The corresponding
potential business for IE manufacturers in the next decade in
the EU has been quantified at about a 10% increase in the
world market on an annual basis [54].
In this context, IE manufacturers should welcome the Pdriven REM NUT process and be involved in any financing
programme at demonstration and development level.
type Amberlite IRA 458 from Rohm&Haas, Philadelphia,
USA
2 type Zeolyst Molecular Sieve13x16x40 from PQ Corporation,
NJ, USA
3 type 1010AO-2AQ from Anaconda Mines, Co.,CA,USA
1
CONCLUSIONS
Deeper understanding and field testing of developing
technology confirm that P-removal and recovery from sewage
and animal waste may be feasible and cost effective, provided
that tailor-made process design as well as plant operation and
control are ensured.
Legislative pressure on the level of P-removal from
wastewater and P content in sludge on one side and
economic drivers such as the wastewater industry striving for
competition, new business opportunities for ion exchange
market and depletion of good quality phosphate rock on the
other are likely to increase general appeal of P-recovery
schemes.
On these premises conventional P recovery methods
based on direct (pre-, sim-, post-) precipitation of insoluble
phosphates by addition of polyvalent ions (Fe3+, Al3+, Ca2+ or
their combination) to P-containing effluents of municipal,
zootechnical or industrial origin are now being challenged by
more engineered processes with higher efficiency and
increased added value of by-products recovered.
Among these latter the so-called P-driven REM NUT
process allows for removal and recovery of almost equimolar
amount of NH4 and PO4 ions from sewage by proper process
design and operation, whereas excess ammonium ion is left to
conventional treatment processes (i.e., bio(de)nitrification).
A further pilot plant investigation of the P-driven REM
NUT process with a 240 m3 d-1 fully automated mobile plant is
now planned in order to assess the following issues:
a) overall economic and technical “robustness” of the
process
b) commercial and agronomic value of "faecal" derived
struvite
c) recovery rate and prompt availability of by-products at
WWTP to satisfy market demand on a large scale.
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