Control of biogas production process by enzymatic and fluorescent image analysis

Figures & data

Figure 1. Digesters of WWTP ‘Kubratovo’.

Table 1. Characteristics of the analysed technologies for biogas production

	Technology	Substrate	Pre-treatment	Temperature mode	Retention time	CCP by place	Season of sampling
WWTP ‘Kubratovo’ – Digester No. 1, 2, 3, 4	One-stage	Sludge	Mechanical	Mesophilic (42 °C)	14.5 days	Inside of the digesters	Summer – in July
WWTP ‘Kubratovo’ – Digester No. 1, 2, 3, 4	One-stage	Sludge	Mechanical	Mesophilic (42 °C)	14.3 days	Inside of the digesters	Autumn– in October

Table 2. Physicochemical and technological parameters of the process in the digesters of WWTP ‘Kubratovo’.

	T°C		pH		COD, mgO2/L		PO4^3−, mg/L		NH4^+, mg/L		ODM, %		FOS/TAC
Parameter	Jul	Oct	Jul	Oct	Jul	Oct	Jul	Oct	Jul	Oct	Jul	Oct	Jul	Oct
D 1	41.7	42.7	7.30	7.42	12394.82	12785.95	88.42	143.41	1479.8	1332.55	53.43	54.26	0.40	0.46
D 2	41.3	41.6	7.44	7.40	13698.60	12134.06	88.25	134.57	1379.83	1299.23	53.61	54.88	0.41	0.34
D 3	42.2	42.7	7.29	7.38	14611.25	12134.06	81.54	120.58	1472.05	1362.00	53.98	55.19	0.31	0.39
D 4	41.5	41.8	7.31	7.33	13568.22	11351.80	88.42	148.41	1470.5	1373.63	53.84	53.74	0.41	0.41

Figure 2. Relationship between the biogas production and aeDHA (a) or anDHA (b) in the eight analysed samples.

Figure 3. Relationship between the biogas production and the ratio aeDHA/anDHA in the eight analysed samples.

Table 3. Fluorescent image analysis of the biological system in the two sampling periods of the four digesters of WWTP ‘Kubratovo’ vs. total and specific biogas production and methane content (%) in the biogas.

*Representative fluorescent images (400× magnification); average values obtained through image analysis in daime program.

Table 4. Correlation between the analysed technological and functional parameters for control and the total and specific biogas production.

	Correlation with total biogas production (m^3/d)			Correlation with specific biogas production (m^3/kg DM/d)
Parameters for control	Pearson coefficient		Level of correlation	Pearson coefficient		Level of correlation
aeDHA	−0.60		High	−0.51		Medium
anDHA	−0.64		High	−0.22		Low
aeDHA:anDHA	0.49		Medium	−0.22		Low
Number:size of clusters	−0.98		High	−0.75		High
Fluorescence intensity	0.44		Medium	0.75		High
Area	0.39		Low	0.74		High
COD	0.35		Low	0.59		Medium
pH	−0.38		Low	−0.13		Low
FOS:TAC	0.37		Low	0.40		Medium
ODM	−0.80		High	−0.63		High
Legend for level of correlation:
		Level of correlation
Negative		Positive
−1.00 < r < −0.60		0.60< r < 1.00			High
−0.59 < r < −0.40		0.40 < r < 0.59			Medium
−0.39 < r < 0		0 < r < 0.39			Low

Figure 4. Fluorescent indicative system for assessment of the effectiveness of anaerobic digesters.

Figure 5. Enlarged part of the chart with the analysed digesters and the area (%) of the fluorescent objects.