ANAEROBIC DIGESTION OF WASTEWATER WITH HIGH SULFATE CONCENTRATION USING MICRO-AERATION AND NATURAL ZEOLITES

Montalvo, S.; Prades, H.; González, M.; Pérez, P.; Guerrero, L.; Huiliñir, C.

doi:10.1590/0104-6632.20160334s20150261

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Selected papers from the XI Latin American Symposium on Anaerobic Digestion (DAAL-2014) • Braz. J. Chem. Eng. 33 (4) • Oct-Dec 2016 • https://doi.org/10.1590/0104-6632.20160334s20150261 copy

ANAEROBIC DIGESTION OF WASTEWATER WITH HIGH SULFATE CONCENTRATION USING MICRO-AERATION AND NATURAL ZEOLITES

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The behavior of anaerobic digestion in batch and UASB reactors using a microaerobic process and natural zeolites was studied. Laboratory assays were carried out across 4 sets of variables: different COD/SO₄^2- ratios, different airflow levels, with and without natural zeolites and room and mesophilic controlled temperatures. The microaerobic process demonstrated hydrogen sulfide removal levels exceeding 90% in most cases, while maintaining the flammable condition of the generated biogas. The level of COD removal exceeded 75% in UASB reactors despite their operation under very low hydraulic retention times (2.8-4.8 hours). The effectiveness of natural zeolites in accelerating UASB reactor startup was demonstrated. Results showing the positive influence of zeolites on the granulation process in UASB reactors were also achieved.

Keywords:
Granulation process; Micro-aeration; Sulfate; Sulfide; Temperature; UASB; Zeolite

Experimental Run I	Experimental Run II	Experimental Run III
COD/SO₄^2-= 5, 10 and 15	COD/SO₄^2-= 5, 10 and 15	COD/SO₄^2-= 1, 5, 10 and 15
Pulse aeration	Pulse aeration	Continuous aeration
Airflow: 0.6, 0.8 and 1.0 mL/d	Airflow: 0, 0.2 and 0.4 mL/d	Airflow: 5, 7.5 and 10 mL/min

COD/SO₄^2-	Glucose (mg/L)	Sodium bicarbonate (mg/L)	Ammonium sulfate (mg/L)	Ammonium phosphate (mg/L)	Total sulfate (mg/L)
15.1	937.5	1000	91.7	17.8	68
10:1	937.5	1000	137.6	27	100
5:1	937.5	1000	275	53	200
1:1	937.5	1000	1375	267	1000

Parameter	Value
Reactor Height (H)	1.22 m
Internal Diameter (D)	0.1 m
Reactor Volume (V)	9.42×10^-3 m³ or 9.42 L
Material	Acrylic

Reactor	Zeolite (L)	Inoculum (L)	Initial SO₄^2- (mg/L)	Temperature (ºC)	Days (Airflow in mL/min)
R1	0	2.8	325	35	1-8 (0)	9-14 (10)	15-20 (14)	21-29 (150)	30-38 (200)
R2	0	2.8	325	19-23	1-8 (0)	9-14 (10)	15-20 (14)	21-29 (150)	30-38 (200)
R3	1.4	1.4	400	35	1-5 (0)	6-14 (100)	15-20 (150)	21-36 (200)
R4	1.4	1.4	400	10-14	1-5 (0)	6-14 (100)	15-20 (150)	21-36 (200)

Component	Composition (%)
SiO₂	67.00
Al₂O₃	13.01
Fe₂O₃	3.60
CaO	3.46
Na₂O	1.32
TiO₂	0.28
MgO	0.78
K₂O	0.53

Micro- aeration (mL/min)	Micro-aeration (vvm)^ Air volume/reactor volume.minute.	COD/SO₄^2- 1	COD/SO₄^2- 5	COD/SO₄^2- 10	COD/SO₄^2- 15
Micro- aeration (mL/min)		Sulfide removal (%)	Sulfide removal (%)	Sulfide removal (%)	Sulfide removal (%)
5	0.005	98.21	81.62	93.50	88.67
7.5	0.0075	98.76	87.38	95.81	87.64
10	0.01	98.29	87.57	90.87	92.42
0	0	0	0	0	0
(Control)

Micro- aeration (mL/min)	Micro-aeration (vvm)^ Air volume/(reactor volume.minute).	COD/SO₄^2- 1	COD/SO₄^2- 5	COD/SO₄^2- 10	COD/SO₄^2- 15
Micro- aeration (mL/min)		Sulfide removal (%)	Sulfide removal (%)	Sulfide removal (%)	Sulfide removal (%)
5	0.005	98.21	81.62	93.50	88.67
7.5	0.0075	98.76	87.38	95.81	87.64
10	0.01	98.29	87.57	90.87	92.42
0	0	0	0	0	0
(Control)

	Concentrations for Aeration Rate = 0 mL/min			Concentrations for Aeration Rate = 200 mL/min
Reactor	SO₄^2-_e (mg/L)	H₂S_e (mg/L)	H₂S_g (mg/L)	SO₄^2-_e (mg/L)	H₂S_e (mg/L)	H₂S_g (mg/L)
R1	150	64	18	185	26	4
R2	165	58	15	200	43	10
R3	164	56	14	163	2	0.1
R4	335	14	11	359	14	2.4

Up-flow velocity (m/h)	COD (mg O₂/L)	SO₄^2- (mg/L)	COD/SO₄^2- ratio	Organic Loading Rate (OLR) (kg COD/m³.d)	HRT (hours)
0.25	1000	400	2.5	5.0	4.8
0.25 (P2)	1500	407	3.69	7.5	4.8
0.25 (P3)	1798	408	4.42	9.0	4.8
0.29 (P4)	1798	408	4.42	10.8	4.0
0.36 (P5)	1798	408	4.42	12.9	3.3
0.36 (P6)	1798	599	3.0	12.9	3.3
0.43 (P7)	1798	599	3.0	15.5	2.8

Disturbance	Average soluble COD removal (%)
Stabilization period	76.92 ± 2.58
P2	80.84 ± 3.65
P3	78.62 ± 2.74
P4	74.09 ± 2.76
P5	72.79 ± 1.83
P6	73.44 ± 2.85
P7	68.26 ± 2.53
P8	65.88 ± 3.05

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(COD)/(SO₄ ^2-) ratio	Chemical Oxygen Demand (g)/SO₄ ^-2 (g)
HRT	Hydraulic Retention Time (hours)
MA	Methanogenic Archea
MAP	Microaerobic Anaerobic Process
R1	UASB reactor operated without natural zeolite at mesophilic temperature (35 ºC)
R2	UASB reactor operated without natural zeolite at room temperature (19-23 ºC)
R3	UASB reactor operated with natural zeolite at mesophilic temperature (35 ºC)
R4	UASB reactor operated with natural zeolite at room temperature (10-14 ºC)
P	Disturbances of operational UASB reactor conditions
OLR	Organic Loading Rates
VSS	Volatile Suspended Solids (mg/L)
vvm	Air volume/minute.volume reactor (L/min.L)