Impact of activated sludge ozonation on filamentous bacteria viability and possible added benefits

Figures & data

Figure 1. Simplified schematic overview of the experimental setup at Klagshamn WWTP.1: Return activated sludge basin of treatment line one 2: Submerged centrifugal pump, 3: Flow meter, 4: Venturi injector, 5: Pressurized reaction vessel (7.9 m³, HRT: ∼18 min), 6: Sample point, 7: Aerated basin of treatment line one.

Table 1. Analysed MPs.

Compound	Compound
TCPP	Triethyl citrate
Triclosan	OTNE
Nonylphenol	Oxybenzone
TBEP	Methylbenzothiazole
AHTN	TPP

Table 2. Sludge characteristics before and after ozone addition.

Trial	Ozone dose (g O3/kg TSS)	TSS (g/L)	DSV (mL)	DSVI (mL/g)	VS (g/L)	CODDissolved (mg/L)	CODTotal (mg/L)
Control	0	5.0	410	82	2.7	81	4750
A	3.0	5.1.	380	74	2.8	141	4590
B	4.0	5.1	280	55	2.8	213	4510
C	4.8	5.1	270	53	2.8	288	4300

Table 3. Characteristics of the sludge as assessed in the quantitative and semi-quantitative microscopy evaluations.

		Trial
Analyses	Scale/unit	Control	A	B	C
Sludge characteristics
Amount of flocs	0-–3	3	3	3	3
Floc shape	*	1 + 3	1	1	1
Bacteria
Filaments in flocs	0–6	3.5	3.5	3.5	3.5
Protruding filaments	0–6	3	2.5	2.5	2
Free bacteria	0–6	1	1	2	2
Protozoa and metazoa
Flagellates	mL^-1	<1000	0	0	0
Free-living ciliates	mL^-1	5600	1000	1400	600
Stalked ciliates	mL^-1	13,200	4800	3000	2400
Rotifers	mL^-1	1400	600	200	200
Live/Dead response
Microthrix (protruding)	0–6	5	3	2	1.5
Type 0041 (protruding)	0–6	5	5	4	4
Microthrix (in flocs)	0–6	5	4	3	3
Type 0041 (in flocs)	0–6	5	5	4	4
Flocs	0–6	5	4	4	4

*Floc shape: 1 = Irregular, 2 = Rounded, 3 = Network.

Figure 2. Live/Dead^® fluorescence microscopy images of the untreated (control) and ozone treated return activated sludges (A–C).

Figure 3. The accumulated methane production (NmL CH₄/g VS_in) during the course of the anaerobic digestion trial with standard deviations.

Figure 4. The reduction of 10 MPs in trials (A–C) compared to the control with standard deviations from trial B.