Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nutrient removal from agricultural run-off in demonstrative full scale
  tubular photobioreactors for microalgae growth   The objective of this paper is to present the design, construction and
operation of 3 full scale semi-closed, horizontal tubular photobioreactors
(PBR) used to remove nutrients of a mixture of agricultural run-off (90%) and
treated domestic wastewater (10%). The microalgal biomass produced in the PBRs
was harvested in a static lamella settling tank. Each PBR treated in average
2.3 m3/d. PBRs were submitted to strong seasonal changes regarding solar
radiation and temperature, which had a direct impact in the activity of
microalgae and the efficiency of the system. Higher mixed liquor pH values were
registered in summer (daily average> 10). Most of the influent and effluent
nitrogen content was inorganic (average of 9.0 mg N/L and 3.17 mg N/L,
respectively), and in the form of nitrate (62% and 50%, respectively). Average
nitrogen removal efficiency was 65%, with values of around 90% in summer, 80%
in autumn, 50 % in winter and 60% in spring. Most of the influent and effluent
phosphorus content was in the form of ortophosphate. Influent average was 0.62
mg P/L, but with great variations and in a considerable number of samples not
detected. Removal efficiency (when influent values were detected) was very high
during all the study, usually greater than 95%, and there were not clear
seasonal trends for efficiency as observed for TIN. Volumetric biomass
production greatly changed between seasons with much lower values in winter (7
g VSS/m3d) than in summer (43 g VSS/m3d). Biomass separation efficiency of the
settler was very good in either terms of turbidity and total suspended solids,
being most of the time lower than 5 UNT and 15 mg/L, respectively. Overall this
study demonstrated the reliable and good effectiveness of microalgae based
technologies such as the PBR to remove nutrients at a full scale size.

18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
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The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
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The categories of this paper are: acc-phys
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The categories of this paper are: stat
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The categories of this paper are: adap-org
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The categories of this paper are: q-fin
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The categories of this paper are: eess
1
The categories of this paper are: cs