Impact of calcination temperature, organic additive percentages, and testing temperature on the rheological behaviour of dried sewage sludge

Bestani, Amar; Lekbir, Choukri; Benmounah, Abdelbaki

doi:10.1515/arh-2024-0025

Figures & Tables

XRD diffractograms of SS0 and SSAs (SSA600, SSA700, SSA750, SSA800, SSA850, SSA900, SSA950, and SSA1000).

(a) Nitrogen adsorption–desorption isotherms and (b) BET specific surface area and average pore diameter of SS0 and SSAs (SSA600, SSA700, SSA750, SSA800, SSA850, SSA900, and SSA950).

SEM images of SS0 and SSAs (SSA600, SSA700, SSA750, SSA800, SSA850, SSA900, SSA950, and SSA1000).

(a) Shear stress (τ)−shear rate (

γ
̇

\dot{\gamma }

) and (b) apparent viscosity (η)−shear rate (

γ
̇

\dot{\gamma }

) curves of SS0 for TS = 4%, at 20°C. — (a) Shear stress (τ)−shear rate ( γ ̇ \dot{\gamma } ) and (b) apparent viscosity (η)−shear rate ( γ ̇ \dot{\gamma } ) curves of SS0 for TS = 4%, at 20°C.

Shear stress (τ)−shear rate (

γ
̇

\dot{\gamma }

) curves of SS0 and SSAs for different TS = 4, 7, 10, 13, and 15%, at 20°C. — Shear stress (τ)−shear rate ( γ ̇ \dot{\gamma } ) curves of SS0 and SSAs for different TS = 4, 7, 10, 13, and 15%, at 20°C.

Apparent viscosity (η)−shear rate (

γ
̇

\dot{\gamma }

) curves of SS0 and SSAs, for different TS = 4, 7, 10, 13, and 15%, at 20°C. — Apparent viscosity (η)−shear rate ( γ ̇ \dot{\gamma } ) curves of SS0 and SSAs, for different TS = 4, 7, 10, 13, and 15%, at 20°C.

Shear stress (τ)−shear rate (

γ
̇

\dot{\gamma }

) curves of SSAs, mixed with organic additives (4% methocel + 4% amijel + 8% starch), for different TS = 4, 7, 10, 13, and 15%, at 20°C. — Shear stress (τ)−shear rate ( γ ̇ \dot{\gamma } ) curves of SSAs, mixed with organic additives (4% methocel + 4% amijel + 8% starch), for different TS = 4, 7, 10, 13, and 15%, at 20°C.

Apparent viscosity (η)−shear rate (

γ
̇

\dot{\gamma }

) curves of SSA, mixed with organic additives (4% methocel + 4% amijel + 8% starch), for different TS = 4, 7, 10, 13, and 15%, at 20°C. — Apparent viscosity (η)−shear rate ( γ ̇ \dot{\gamma } ) curves of SSA, mixed with organic additives (4% methocel + 4% amijel + 8% starch), for different TS = 4, 7, 10, 13, and 15%, at 20°C.

Shear stress (τ)−shear rate (

γ
̇

\dot{\gamma }

) curves of sewage sludge ash SSA850, mixed with organic additives (4% amijel + 8% starch) and various percentages of methocel: 3, 4, 5, and 6%, for different TS, at 20°C. — Shear stress (τ)−shear rate ( γ ̇ \dot{\gamma } ) curves of sewage sludge ash SSA850, mixed with organic additives (4% amijel + 8% starch) and various percentages of methocel: 3, 4, 5, and 6%, for different TS, at 20°C.

Apparent viscosity (η)−shear rate (

γ
̇

\dot{\gamma }

) curves of sewage sludge ash SSA850, mixed with organic additives (4% amijel + 8% starch) and various percentages of methocel: 3, 4, 5, and 6%, for different TS, at 20°C. — Apparent viscosity (η)−shear rate ( γ ̇ \dot{\gamma } ) curves of sewage sludge ash SSA850, mixed with organic additives (4% amijel + 8% starch) and various percentages of methocel: 3, 4, 5, and 6%, for different TS, at 20°C.

Shear stress (τ)−shear rate (

γ
̇

\dot{\gamma }

) curves of sludge systems (SS0, SSA850, SSA850 + 4% methocel + 4% amijel + 8% starch, and SSA850 + 5% methocel + 4% amijel + 8% starch) for a TS = 10%, at different testing temperatures (20, 30, 40, 50, and 60°C). — Shear stress (τ)−shear rate ( γ ̇ \dot{\gamma } ) curves of sludge systems (SS0, SSA850, SSA850 + 4% methocel + 4% amijel + 8% starch, and SSA850 + 5% methocel + 4% amijel + 8% starch) for a TS = 10%, at different testing temperatures (20, 30, 40, 50, and 60°C).

Apparent viscosity (η)−shear rate (

γ
̇

\dot{\gamma }

) curves of sludge systems (SS0, SSA850, SSA850 + 4% methocel + 4% amijel + 8% starch, and SSA850 + 5% methocel + 4% amijel + 8% starch) for a TS = 10%, at different testing temperatures (20, 30, 40, 50, and 60°C). — Apparent viscosity (η)−shear rate ( γ ̇ \dot{\gamma } ) curves of sludge systems (SS0, SSA850, SSA850 + 4% methocel + 4% amijel + 8% starch, and SSA850 + 5% methocel + 4% amijel + 8% starch) for a TS = 10%, at different testing temperatures (20, 30, 40, 50, and 60°C).

Arrhenius plots of ln(η) versus 1/T for sludge systems (SS0, SSA850, SSA850 mixed with 4% methocel + 4% amijel + 8% starch, and SSA850 mixed with 5% methocel + 4% amijel + 8% starch), at TS = 10%.

Fitting parameters of different viscosity rheological models for different TS of SS0 and SSAs at 20°C

Sludge	TS (%)	Cross model					Carreau model
		η = η ∞ + ( η 0 ‒ η ∞ ) 1 + ( λ γ ̇ ) m \eta ={\eta }_{\infty }+\frac{({\eta }_{0}‒{\eta }_{\infty })}{1+{(\lambda \dot{\gamma })}^{m}}					η = η ∞ + ( η 0 ‒ η ∞ ) ( 1 + ( λ γ ̇ ) 2 ) n ‒ 1 2 \eta ={\eta }_{\infty }+\left[({\eta }_{0}‒{\eta }_{\infty }){(1+{(\lambda \dot{\gamma })}^{2})}^{\frac{n‒1}{2}}\hspace{.25em}\right]
		η ∞ {\eta }_{\infty } (Pa s)	η 0 {\eta }_{0} (Pa s)	λ \lambda (s)	m	R ²	η ∞ {\eta }_{\infty } (Pa s)	η 0 {\eta }_{0} (Pa s)	λ \lambda (s)	n	R ²
SS0	4	1.967 × 10⁻³	1.45	11.64	1.15	1.0000	1.547 × 10⁻³	1.18	16.01	7.00 × 10⁻⁴	0.9906
	7	2.268 × 10⁻³	1.05	14.71	1.00	0.9964	2.288 × 10⁻³	0.69	10.10	6.84 × 10⁻⁴	0.9947
	10	2.280 × 10⁻³	0.59	13.16	0.95	0.9985	2.336 × 10⁻³	0.05	0.71	7.59 × 10⁻⁴	0.9920
	13	2.760 × 10⁻³	0.92	11.34	1.01	1.0000	2.760 × 10⁻³	0.23	2.93	7.46 × 10⁻⁴	0.9971
	15	3.310 × 10⁻³	0.21	3.05	0.97	1.0000	3.372 × 10⁻³	0.06	0.78	7.87 × 10⁻⁴	0.9976
SSA800	4	1.208 × 10⁻³	0.54	10.85	0.99	1.0000	1.245 × 10⁻³	0.10	1.95	7.49 × 10⁻⁴	0.9986
	7	1.444 × 10⁻³	0.66	11.49	1.03	0.9989	1.388 × 10⁻³	0.20	3.87	5.93 × 10⁻⁴	0.9938
	10	1.587 × 10⁻³	0.50	9.26	0.98	1.0000	1.552 × 10⁻³	0.05	0.79	7.55 × 10⁻⁴	0.9956
	13	1.982 × 10⁻³	0.13	1.98	0.92	1.0000	2.203 × 10⁻³	0.04	0.54	9.40 × 10⁻⁴	0.9985
	15	2.264 × 10⁻³	0.18	2.08	0.90	1.0000	2.542 × 10⁻³	0.07	0.72	7.56 × 10⁻⁴	0.9969
SSA850	4	1.167 × 10⁻³	0.16	3.49	0.96	1.0000	1.062 × 10⁻³	0.05	1.10	1.15 × 10⁻⁴	0.9897
	7	1.242 × 10⁻³	0.43	7.51	1.03	1.0000	1.241 × 10⁻³	0.13	2.47	5.89 × 10⁻⁴	0.9979
	10	1.267 × 10⁻³	0.41	6.20	1.00	0.9990	1.237 × 10⁻³	0.06	0.85	7.56 × 10⁻⁴	0.9881
	13	1.695 × 10⁻³	0.20	2.95	0.97	1.0000	1.566 × 10⁻³	0.05	0.69	8.01 × 10⁻⁴	0.9941
	15	2.128 × 10⁻³	0.11	1.49	0.90	1.0000	1.830 × 10⁻³	0.06	0.78	7.29 × 10⁻⁴	0.9918
SSA900	4	1.164 × 10⁻³	0.23	3.98	1.04	1.0000	1.250 × 10⁻³	0.10	1.90	7.45 × 10⁻⁴	0.9974
	7	1.237 × 10⁻³	0.29	4.63	1.05	1.0000	1.202 × 10⁻³	0.24	4.75	7.04 × 10⁻⁴	0.9984
	10	1.268 × 10⁻³	0.31	6.10	0.95	0.9994	1.394 × 10⁻³	0.05	0.87	7.47 × 10⁻⁴	0.9939
	13	1.332 × 10⁻³	0.25	3.99	0.96	1.0000	1.418 × 10⁻³	0.06	0.86	8.06 × 10⁻⁴	0.9978
	15	1.854 × 10⁻³	0.12	1.54	0.90	0.9992	2.480 × 10⁻³	0.06	0.76	1.07 × 10⁻³	0.9936
SSA950	4	1.162 × 10⁻³	0.24	3.90	1.03	1.0000	1.193 × 10⁻³	0.10	1.76	9.99 × 10⁻⁴	0.9941
	7	1.233 × 10⁻³	0.26	4.26	1.04	0.9995	1.208 × 10⁻³	0.24	4.69	9.76 × 10⁻⁴	0.9246
	10	1.248 × 10⁻³	0.17	3.96	0.93	0.9993	1.261 × 10⁻³	0.04	0.70	1.00 × 10⁻³	0.9973
	13	1.355 × 10⁻³	0.17	3.01	0.91	1.0000	1.608 × 10⁻³	0.05	0.69	1.00 × 10⁻³	0.9961
	15	1.361 × 10⁻³	0.13	1.65	1.04	0.9997	1.291 × 10⁻³	0.05	0.74	1.00 × 10⁻³	0.9986

Fitting parameters of different shear stress rheological models for different TS of SSA850, mixed with organic additives (4% amijel + 8% starch) and various percentages of methocel: 3, 4, 5, and 6%, at 20°C

Sludge	TS (%)	Herschel–Bulkley model				Ostwald–de Waele model			Thixotropy
		τ = τ 0 + K γ n \tau ={\tau }_{0}+K{\gamma }^{n}				τ = K γ n \tau =K{\gamma }^{n}			Thixotropy
		τ ₀ (Pa)	K (Pa s)	n	R ²	K (Pa s)	n	R ²	rHa (Pa s⁻¹)
SSA850 + 3% methocel + 4% amijel + 8% starch	4	0.1117	7.97 × 10⁻⁶	1.9683	0.9993	3.97 × 10⁻⁵	1.7211	0.9949	NT
	7	0.3205	6.56 × 10⁻⁶	2.0215	0.9956	3.06 × 10⁻⁴	1.4294	0.9728	NT
	10	0.2465	1.42 × 10⁻⁴	1.6243	0.9990	5.79 × 10⁻⁴	1.4091	0.9950	NT
	13	0.5263	5.27 × 10⁻⁴	1.4941	0.9991	2.69 × 10⁻³	1.2460	0.9932	NT
	15	0.7269	1.54 × 10⁻³	1.3971	0.9993	5.78 × 10⁻³	1.1968	0.9951	NT
SSA850 + 4% methocel + 4% amijel + 8% starch	4	0.1423	9.44 × 10⁻⁴	1.2445	0.9966	2.54 × 10⁻³	1.0953	0.9941	41.14
	7	0.2324	4.64 × 10⁻³	1.0786	0.9997	1.02 × 10⁻²	0.9613	0.9978	69.48
	10	0.0738	3.54 × 10⁻²	0.8898	0.9999	3.88 × 10⁻²	0.8764	0.9999	175.48
	13	−0.3084	1.64 × 10⁻¹	0.7735	0.9999	1.41 × 10⁻¹	0.7952	0.9998	241.47
	15	−0.3487	1.73 × 10⁻¹	0.7659	0.9999	1.47 × 10⁻¹	0.7900	0.9998	NT
SSA850 + 5% methocel + 4% amijel + 8% starch	4	0.1618	2.10 × 10⁻³	1.1285	0.9990	5.31 × 10⁻³	0.9897	0.9966	NT
	7	0.1035	1.47 × 10⁻²	0.9779	1.0000	1.79 × 10⁻²	0.9491	0.9998	NT
	10	−0.2135	8.02 × 10⁻²	0.8297	0.9998	6.83 × 10⁻²	0.8531	0.9997	NT
	13	−0.5515	2.97 × 10⁻¹	0.7552	0.9999	2.53 × 10⁻¹	0.7786	0.9998	NT
	15	−0.9060	6.48 × 10⁻¹	0.7163	0.9997	5.60 × 10⁻¹	0.7374	0.9996	NT
SSA850 + 6% methocel + 4% amijel + 8% starch	4	0.1208	2.15 × 10⁻³	1.1360	0.9993	4.42 × 10⁻³	1.0284	0.9979	NT
	7	0.1226	1.78 × 10⁻²	0.9539	0.9999	2.21 × 10⁻²	0.9220	0.9997	NT
	10	−0.0702	1.20 × 10⁻¹	0.8106	0.9999	1.05 × 10⁻¹	0.8304	0.9999	NT
	13	−0.2255	8.35 × 10⁻¹	0.6900	0.9993	6.70 × 10⁻¹	0.7215	0.9991	NT
	15	−0.7781	8.19 × 10⁻¹	0.7039	0.9985	8.26 × 10⁻¹	0.7025	0.9985	NT

Chemical composition and weight LOI of SS0 and SSAs

Compounds (wt%)	Dried sludge and sludge ashes
Compounds (wt%)	SS0	SSA600	SSA700	SSA750	SSA800	SSA850	SSA900	SSA950
Na₂O	0.250	0.380	0.360	0.390	0.380	0.420	0.400	0.410
MgO	1.640	2.910	2.960	3.020	3.010	3.030	3.050	3.080
Al₂O₃	6.420	11.770	12.080	12.160	12.170	12.180	12.200	12.260
SiO₂	15.520	30.700	33.120	32.550	32.580	32.830	33.140	32.890
P₂O₅	5.270	9.390	9.870	10.050	10.070	10.150	10.220	10.220
SO₃	3.300	4.730	4.680	4.770	5.000	5.140	5.150	5.170
K₂O	0.950	1.830	1.890	1.830	1.840	1.860	1.790	1.770
CaO	11.550	21.990	22.890	22.920	22.940	23.490	24.140	24.380
TiO₂	0.330	0.680	0.690	0.700	0.700	0.700	0.700	0.720
MnO	0.150	0.290	0.290	0.300	0.320	0.320	0.320	0.320
Fe₂O₃	2.580	5.520	5.660	5.680	5.700	5.920	6.020	6.030
Cr₂O₃	0.007	0.010	0.010	0.020	0.020	0.020	0.020	0.020
NiO	0.005	0.009	0.010	0.010	0.009	0.010	0.010	0.010
CuO	0.020	0.040	0.040	0.000	0.000	0.040	0.040	0.040
ZnO	0.060	0.140	0.150	0.150	0.160	0.160	0.170	0.170
SrO	0.020	0.040	0.050	0.050	0.060	0.070	0.070	0.070
Rb₂O	0.002	0.005	0.005	0.005	0.006	0.006	0.007	0.006
PbO	0.004	0.010	0.010	0.010	0.020	0.020	0.020	0.020
BaO	0.040	0.090	0.100	0.100	0.100	0.100	0.100	0.110
ZrO₂	0.002	0.005	0.006	0.006	0.008	0.009	0.010	0.010
Cl	0.100	0.100	0.120	0.110	0.100	0.090	0.060	0.050
LOI	52.010	10.060	5.020	5.560	5.760	3.880	3.110	2.540

Fitting parameters of different shear stress rheological models for different TS of SS0 and SSAs at 20°C

Sludge	TS (%)	Herschel–Bulkley model				Ostwald–de Waele model
		τ = τ 0 + K γ n \tau ={\tau }_{0}+K{\gamma }^{n}				τ = K γ n \tau =K{\gamma }^{n}
		τ ₀ (Pa)	K (Pa s)	n	R ²	K (Pa s)	n	R ²
SS0	4	0.1123	6.43 × 10⁻⁵	1.6082	0.9992	2.93 × 10⁻⁴	1.3765	0.9944
	7	0.1584	5.20 × 10⁻⁵	1.6558	0.9981	3.82 × 10⁻⁴	1.3510	0.9900
	10	0.1628	2.15 × 10⁻⁵	1.8161	0.9976	1.61 × 10⁻⁴	1.5076	0.9900
	13	0.2282	1.62 × 10⁻⁵	1.8736	0.9955	2.39 × 10⁻⁴	1.4594	0.9834
	15	0.2413	7.17 × 10⁻⁵	1.6555	0.9958	7.39 × 10⁻⁴	1.2872	0.9854
SSA800	4	0.0640	6.65 × 10⁻⁵	1.5952	0.9992	1.67 × 10⁻⁴	1.4551	0.9973
	7	0.0699	5.73 × 10⁻⁵	1.6302	0.9993	1.49 × 10⁻⁴	1.4844	0.9973
	10	0.0846	5.81 × 10⁻⁵	1.6344	0.9989	1.75 × 10⁻⁴	1.4665	0.9962
	13	0.1545	4.82 × 10⁻⁵	1.6764	0.9986	3.15 × 10⁻⁴	1.3896	0.9915
	15	0.2013	5.36 × 10⁻⁵	1.6634	0.9980	5.45 × 10⁻⁴	1.3086	0.9872
SSA850	4	0.0670	6.46 × 10⁻⁵	1.5974	0.9991	1.71 × 10⁻⁴	1.4489	0.9970
	7	0.0645	5.99 × 10⁻⁵	1.6169	0.9991	1.49 × 10⁻⁴	1.4781	0.9973
	10	0.0698	5.63 × 10⁻⁵	1.6359	0.9992	1.44 × 10⁻⁴	1.4926	0.9972
	13	0.1135	5.37 × 10⁻⁵	1.6532	0.9992	3.15 × 10⁻⁴	1.4352	0.9948
	15	0.1855	4.47 × 10⁻⁵	1.6948	0.9984	3.92 × 10⁻⁴	1.3622	0.9890
SSA900	4	0.0615	7.46 × 10⁻⁵	1.5755	0.9990	1.80 × 10⁻⁴	1.4417	0.9973
	7	0.0665	4.77 × 10⁻⁵	1.6548	0.9994	1.24 × 10⁻⁴	1.5092	0.9975
	10	0.0768	5.10 × 10⁻⁵	1.6507	0.9990	1.58 × 10⁻⁴	1.4788	0.9967
	13	0.0941	4.03 × 10⁻⁵	1.7012	0.9992	1.36 × 10⁻⁴	1.5153	0.9960
	15	0.1729	5.53 × 10⁻⁵	1.6554	0.9983	4.25 × 10⁻⁴	1.3438	0.9898
SSA950	4	0.0640	6.91 × 10⁻⁵	1.5860	0.9992	4.84 × 10⁻³	1.4441	0.9973
	7	0.0629	5.34 × 10⁻⁵	1.6364	0.9992	1.30 × 10⁻⁴	1.5001	0.9975
	10	0.0657	3.98 × 10⁻⁵	1.6962	0.9991	9.70 × 10⁻⁵	1.5599	0.9974
	13	0.1012	3.90 × 10⁻⁵	1.7070	0.9988	1.43 × 10⁻⁴	1.5086	0.9952
	15	0.1097	5.22 × 10⁻⁵	1.6521	0.9991	1.49 × 10⁻⁴	1.4919	0.9967

Fitting parameters of different viscosity rheological models for different TS of SSA, mixed with organic additives (4% methocel + 4% amijel + 8% starch), at 20°C

Sludge	TS (%)	Cross model					Carreau model
		η = η ∞ + ( η 0 ‒ η ∞ ) 1 + ( λ γ ̇ ) m \eta ={\eta }_{\infty }+\frac{({\eta }_{0}‒{\eta }_{\infty })}{1+{(\lambda \dot{\gamma })}^{m}}					η = η ∞ + ( η 0 ‒ η ∞ ) ( 1 + ( λ γ ̇ ) 2 ) n ‒ 1 2 \eta ={\eta }_{\infty }+\left[({\eta }_{0}‒{\eta }_{\infty }){(1+{(\lambda \dot{\gamma })}^{2})}^{\frac{n‒1}{2}}\hspace{.25em}\right]
		η ∞ {\eta }_{\infty } (Pa s)	η 0 {\eta }_{0} (Pa s)	λ \lambda (s)	M	R ²	η ∞ {\eta }_{\infty } (Pa s)	η 0 {\eta }_{0} (Pa s)	λ \lambda (s)	n	R ²
SSA800 + 4% methocel + 4% amijel + 8% starch	4	3.810 × 10⁻³	0.85	12.26	1.00	0.9979	3.817 × 10⁻³	0.16	2.31	1.79 × 10⁻⁴	0.9968
	7	8.071 × 10⁻³	0.86	14.64	0.84	1.0000	8.517 × 10⁻³	0.09	0.62	1.80 × 10⁻⁴	0.9939
	10	1.926 × 10⁻²	0.55	6.38	0.80	0.9960	1.891 × 10⁻²	0.70	12.89	2.59 × 10⁻¹	0.9978
	13	5.496 × 10⁻²	0.65	2.61	0.79	1.0000	5.317 × 10⁻²	0.42	2.19	3.10 × 10⁻¹	0.9987
	15	7.422 × 10⁻²	0.81	3.71	0.67	0.9994	8.580 × 10⁻²	0.24	0.31	1.80 × 10⁻⁴	0.9963
SSA850 + 4% methocel + 4% amijel + 8% starch	4	4.300 × 10⁻³	1.09	6.89	1.27	0.9830	3.981 × 10⁻³	1.02	14.38	2.89 × 10⁻⁴	0.9289
	7	7.752 × 10⁻³	3.35	8.90	1.15	0.9955	6.991 × 10⁻³	1.67	7.13	6.72 × 10⁻⁵	0.9687
	10	1.854 × 10⁻²	1.66	7.90	0.96	1.0000	1.862 × 10⁻²	1.22	5.38	1.53 × 10⁻⁴	0.9993
	13	4.781 × 10⁻²	0.75	4.33	0.77	1.0000	4.644 × 10⁻²	0.42	2.82	3.13 × 10⁻¹	0.9996
	15	5.021 × 10⁻²	0.82	3.85	0.83	0.9996	4.868 × 10⁻²	0.55	3.29	2.55 × 10⁻¹	0.9983
SSA900 + 4% methocel + 4% amijel + 8% starch	4	4.583 × 10⁻³	1.27	17.48	1.00	1.0000	4.587 × 10⁻³	0.23	3.22	1.01 × 10⁻⁴	0.9969
	7	9.014 × 10⁻³	0.25	4.63	0.83	0.9947	8.943 × 10⁻³	0.10	1.77	2.13 × 10⁻¹	1.0000
	10	2.785 × 10⁻²	0.59	15.98	0.65	0.9971	2.743 × 10⁻²	0.21	3.76	3.94 × 10⁻¹	0.9994
	13	5.656 × 10⁻²	0.78	24.11	0.45	0.9982	5.279 × 10⁻²	0.30	3.92	6.13 × 10⁻¹	0.9973
	15	8.044 × 10⁻²	0.56	3.13	0.56	1.0000	7.369 × 10⁻²	0.30	1.68	5.63 × 10⁻¹	0.9985
SSA950 + 4% methocel + 4% amijel + 8% starch	4	4.731 × 10⁻³	0.99	16.60	0.99	1.0000	4.699 × 10⁻³	0.96	18.22	3.79 × 10⁻²	0.9961
	7	9.989 × 10⁻³	0.30	5.34	0.85	0.9962	9.926 × 10⁻³	0.15	2.78	1.91 × 10⁻¹	0.9991
	10	2.770 × 10⁻²	0.50	6.80	0.72	0.9983	2.831 × 10⁻²	0.12	0.63	2.34 × 10⁻¹	0.9984
	13	5.708 × 10⁻²	0.51	6.68	0.35	1.0000	3.861 × 10⁻²	0.31	6.91	7.69 × 10⁻¹	0.9988
	15	1.108 × 10⁻¹	0.34	0.15	0.60	0.9965	6.329 × 10⁻²	0.30	0.67	7.64 × 10⁻¹	0.9953

Fitting parameters of different viscosity rheological models for a TS = 10% of SS0, SSA850, SSA850 + 4% methocel + 4% amijel + 8% starch, and SSA850 + 5% methocel + 4% amijel + 8% starch at different testing temperatures (20, 30, 40, 50, and 60°C)

Sludge	T (°C)	Cross model					Carreau model
		η = η ∞ + ( η 0 ‒ η ∞ ) 1 + ( λ γ ̇ ) m \eta ={\eta }_{\infty }+\frac{({\eta }_{0}‒{\eta }_{\infty })}{1+{(\lambda \dot{\gamma })}^{m}}					η = η ∞ + ( η 0 ‒ η ∞ ) ( 1 + ( λ γ ̇ ) 2 ) n ‒ 1 2 \eta ={\eta }_{\infty }+\left[({\eta }_{0}‒{\eta }_{\infty }){(1+{(\lambda \dot{\gamma })}^{2})}^{\frac{n‒1}{2}}\hspace{.25em}\right]
		η ∞ {\eta }_{\infty } (Pa s)	η 0 {\eta }_{0} (Pa s)	λ \lambda (s)	m	R ²	η ∞ {\eta }_{\infty } (Pa s)	η 0 {\eta }_{0} (Pa s)	λ \lambda (s)	n	R ²
SS0	20	2.28 × 10⁻³	0.59	13.16	0.95	0.9985	2.336 × 10⁻³	0.05	0.71	7.59 × 10⁻⁴	0.9920
	30	1.556 × 10⁻³	0.43	5.33	1.03	0.9987	1.510 × 10⁻³	0.39	5.68	6.91 × 10⁻⁴	0.9982
	40	1.258 × 10⁻³	0.20	3.57	0.97	1.0000	1.353 × 10⁻³	0.06	0.95	1.00 × 10⁻³	0.9988
	50	1.006 × 10⁻³	0.09	1.43	1.03	1.0000	1.010 × 10⁻³	0.04	0.73	7.47 × 10⁻⁴	0.9980
	60	1.017 × 10⁻³	0.10	1.51	1.07	0.9982	7.905 × 10⁻⁴	0.06	1.07	1.79 × 10⁻⁴	0.9989
SSA850	20	1.267 × 10⁻³	0.41	6.20	1.00	0.9990	1.237 × 10⁻³	0.06	0.85	7.56 × 10⁻⁴	0.9881
	30	1.175 × 10⁻³	0.09	1.38	1.07	0.9994	1.105 × 10⁻³	0.05	0.87	7.53 × 10⁻⁴	0.9969
	40	1.126 × 10⁻³	0.15	2.01	1.11	1.0000	9.833 × 10⁻⁴	0.23	4.52	6.65 × 10⁻⁴	0.9979
	50	1.030 × 10⁻³	0.26	3.78	1.09	1.0000	8.731 × 10⁻⁴	0.46	9.00	4.63 × 10⁻⁴	0.9927
	60	9.888 × 10⁻⁴	0.14	1.87	1.13	0.9987	7.800 × 10⁻⁴	0.31	5.91	1.77 × 10⁻⁴	0.9973
SSA850 + 4% methocel + 4% amijel + 8% starch	20	1.854 × 10⁻²	1.66	7.90	0.96	1.0000	1.862 × 10⁻²	1.22	5.38	1.53 × 10⁻⁴	0.9993
	30	1.230 × 10⁻²	0.25	2.25	0.78	1.0000	1.208 × 10⁻²	0.11	1.01	2.80 × 10⁻¹	0.9997
	40	9.526 × 10⁻³	0.16	1.86	0.86	0.9967	9.319 × 10⁻³	0.18	3.96	2.47 × 10⁻¹	0.9961
	50	7.444 × 10⁻³	0.08	0.55	1.16	0.9933	7.328 × 10⁻³	0.06	0.61	7.49 × 10⁻⁴	0.9923
	60	5.679 × 10⁻³	0.05	0.38	1.44	0.9782	5.494 × 10⁻³	0.36	6.30	1.74 × 10⁻⁴	0.9592
SSA850 + 5% methocel + 4% amijel + 8% starch	20	2.762 × 10⁻²	0.79	28.88	0.62	0.9974	3.043 × 10⁻²	0.09	0.29	5.00 × 10⁻⁴	0.9701
	30	2.092 × 10⁻²	0.26	2.33	0.75	1.0000	2.019 × 10⁻²	0.13	1.19	3.44 × 10⁻¹	1.0028
	40	1.357 × 10⁻²	0.28	7.17	0.67	0.9999	1.334 × 10⁻²	0.22	7.68	3.90 × 10⁻¹	0.9963
	50	1.048 × 10⁻²	0.20	3.12	0.83	0.9950	1.043 × 10⁻²	0.08	1.04	2.12 × 10⁻¹	0.9930
	60	8.577 × 10⁻³	0.06	0.35	1.37	0.9766	8.378 × 10⁻³	0.07	0.82	1.79 × 10⁻⁴	0.9700

Fitting parameters of different shear stress rheological models for different TS of SSAs mixed with organic additives (4% methocel + 4% amijel + 8% starch) at 20°C

Sludge	TS (%)	Herschel–Bulkley model				Ostwald–de Waele model			Thixotropy
		τ = τ 0 + K γ n \tau ={\tau }_{0}+K{\gamma }^{n}				τ = K γ n \tau =K{\gamma }^{n}			Thixotropy
		τ ₀ (Pa)	K (Pa s)	n	R ²	K (Pa s)	n	R ²	rHa (Pa s⁻¹)
SSA800 + 4% methocel + 4% amijel + 8% starch	4	0.2306	1.96 × 10⁻⁴	1.4864	0.9913	1.50 × 10⁻³	1.1813	0.9834	18.87
	7	0.1844	6.21 × 10⁻³	1.0490	0.9998	1.08 × 10⁻²	0.9665	0.9989	82.19
	10	−0.0500	4.39 × 10⁻²	0.8634	0.9998	4.15 × 10⁻²	0.8718	0.9998	242.35
	13	−0.7437	2.50 × 10⁻¹	0.7275	0.9996	1.85 × 10⁻¹	0.7707	0.9993	525.66
	15	−0.7322	3.12 × 10⁻¹	0.7432	0.9999	2.51 × 10⁻¹	0.7746	0.9997	NT
SSA850 + 4% methocel + 4% amijel + 8% starch	4	0.1423	9.44 × 10⁻⁴	1.2445	0.9966	2.54 × 10⁻³	1.0953	0.9941	41.14
	7	0.2324	4.64 × 10⁻³	1.0786	0.9997	1.02 × 10⁻²	0.9613	0.9978	69.48
	10	0.0738	3.54 × 10⁻²	0.8898	0.9999	3.88 × 10⁻²	0.8764	0.9999	175.48
	13	−0.3084	1.64 × 10⁻¹	0.7735	0.9999	1.41 × 10⁻¹	0.7952	0.9998	241.47
	15	−0.3487	1.73 × 10⁻¹	0.7659	0.9999	1.47 × 10⁻¹	0.7900	0.9998	NT
SSA900 + 4% methocel + 4% amijel + 8% starch	4	0.1372	2.29 × 10⁻³	1.1097	0.9987	5.10 × 10⁻³	0.9891	0.9968	58.18
	7	0.1416	7.57 × 10⁻³	1.0329	0.9999	1.11 × 10⁻²	0.9756	0.9994	58.77
	10	−0.2419	8.86 × 10⁻²	0.8036	0.9998	7.35 × 10⁻²	0.8310	0.9997	268.27
	13	−0.4811	2.66 × 10⁻¹	0.7452	0.9998	2.26 × 10⁻¹	0.7690	0.9997	233.02
	15	−0.7838	3.96 × 10⁻¹	0.7082	0.9999	3.19 × 10⁻¹	0.7394	0.9997	NT
SSA950 + 4% methocel + 4% amijel + 8% starch	4	0.1230	2.42 × 10⁻³	1.1084	0.9993	4.80 × 10⁻³	1.0048	0.9979	56.79
	7	0.1301	8.77 × 10⁻³	1.0246	0.9999	1.21 × 10⁻²	0.9770	0.9996	58.35
	10	−0.2068	8.23 × 10⁻²	0.8149	0.9998	6.99 × 10⁻²	0.8387	0.9997	219.88
	13	−1.4948	5.41 × 10⁻¹	0.6644	0.9997	3.70 × 10⁻¹	0.7185	0.9991	NT
	15	−1.4462	6.94 × 10⁻¹	0.6836	0.9997	5.36 × 10⁻¹	0.7205	0.9995	NT

Fitting parameters of different shear stress rheological models for a TS = 10% of SS0, SSA850, SSA850 mixed with 4% methocel + 4% amijel + 8% starch, and SSA850 mixed with 5% methocel + 4% amijel + 8% starch, at different testing temperatures (20, 30, 40, 50, and 60°C)

Sludge system	T (°C)	Herschel–Bulkley model				Ostwald–de Waele model			Thixotropy
		τ = τ 0 + K γ n \tau ={\tau }_{0}+K{\gamma }^{n}				τ = K γ n \tau =K{\gamma }^{n}			Thixotropy
		τ ₀ (Pa)	K (Pa s)	n	R ²	K (Pa s)	n	R ²	rHa (Pa s⁻¹)
SS0	20	0.1628	2.15 × 10⁻⁵	1.8161	0.9976	1.61 × 10⁻⁴	1.5076	0.9900	NT
	30	0.1128	1.63 × 10⁻⁵	1.8572	0.9994	7.16 × 10⁻⁵	1.6296	0.9953	NT
	40	0.0846	2.03 × 10⁻⁵	1.8243	0.9992	6.01 × 10⁻⁵	1.6581	0.9969	NT
	50	0.0836	1.29 × 10⁻⁵	1.8677	0.9994	4.85 × 10⁻⁵	1.6638	0.9962	NT
	60	0.0661	2.64 × 10⁻⁵	1.7487	0.9993	7.23 × 10⁻⁵	1.5945	0.9972	NT
SSA850	20	0.0698	5.63 × 10⁻⁵	1.6359	0.9992	1.44 × 10⁻⁴	1.4926	0.9972	NT
	30	0.0609	3.92 × 10⁻⁵	1.6861	0.9993	9.55 × 10⁻⁵	1.5501	0.9976	NT
	40	0.0397	1.04 × 10⁻⁴	1.5204	0.9986	1.81 × 10⁻⁴	1.4354	0.9979	NT
	50	0.0275	1.96 × 10⁻⁴	1.3989	0.9973	2.93 × 10⁻⁴	1.3383	0.9969	NT
	60	0.0409	1.75 × 10⁻⁴	1.3898	0.9986	3.52 × 10⁻⁴	1.2838	0.9973	NT
SSA850 + 4% methocel + 4% amijel + 8% starch	20	0.0738	3.54 × 10⁻²	0.8898	0.9999	3.88 × 10⁻²	0.8764	0.9999	175.48
	30	0.2021	1.60 × 10⁻²	0.9644	0.9998	2.31 × 10⁻²	0.9095	0.9994	111.92
	40	0.2005	6.94 × 10⁻³	1.0533	0.9996	1.18 × 10⁻²	0.9743	0.9988	59.04
	50	0.1598	3.74 × 10⁻³	1.1101	0.9997	1.57 × 10⁻⁴	0.0039	0.9987	NT
	60	0.1398	1.31 × 10⁻³	1.2387	0.9997	2.72 × 10⁻³	1.1293	0.9983	NT
SSA850 + 5% methocel + 4% amijel + 8% starch	20	−0.2135	8.02 × 10⁻²	0.8297	0.9998	6.83 × 10⁻²	0.8531	0.9997	NT
	30	0.0962	4.32 × 10⁻²	0.8711	1.0000	4.81 × 10⁻²	0.8554	0.9999	NT
	40	0.1929	1.61 × 10⁻²	0.9813	0.9998	2.23 × 10⁻²	0.9333	0.9995	NT
	50	0.1875	8.13 × 10⁻³	1.0435	0.9998	1.27 × 10⁻²	0.9767	0.9991	NT
	60	0.2102	2.52 × 10⁻³	1.1967	0.9995	5.15 × 10⁻³	1.0893	0.9981	NT

Fitting parameters of different viscosity rheological models for different TS of SSA850, mixed with organic additives (4% amijel + 8% starch) and various percentages of methocel: 3, 4, 5, and 6%, at 20°C

Sludge	TS (%)	Cross model					Carreau model
		η = η ∞ + ( η 0 ‒ η ∞ ) 1 + ( λ γ ̇ ) m \eta ={\eta }_{\infty }+\frac{({\eta }_{0}‒{\eta }_{\infty })}{1+{(\lambda \dot{\gamma })}^{m}}					η = η ∞ + ( η 0 ‒ η ∞ ) ( 1 + ( λ γ ̇ ) 2 ) n ‒ 1 2 \eta ={\eta }_{\infty }+\left[({\eta }_{0}‒{\eta }_{\infty }){(1+{(\lambda \dot{\gamma })}^{2})}^{\frac{n‒1}{2}}\hspace{.25em}\right]
		η ∞ {\eta }_{\infty } (Pa s)	η 0 {\eta }_{0} (Pa s)	λ \lambda (s)	m	R ²	η ∞ {\eta }_{\infty } (Pa s)	η 0 {\eta }_{0} (Pa s)	λ \lambda (s)	n	R ²
SSA850 + 3% methocel + 4% amijel + 8% starch	4	1.246 × 10⁻³	0.06	0.43	1.24	0.9992	8.456 × 10⁻⁴	0.05	0.56	7.58 × 10⁻⁴	0.9987
	7	2.807 × 10⁻³	0.12	0.45	1.16	0.9978	2.461 × 10⁻³	0.09	0.49	7.48 × 10⁻⁴	0.9976
	10	4.982 × 10⁻³	0.06	0.22	1.55	0.9977	4.184 × 10⁻³	0.06	0.44	7.60 × 10⁻⁴	0.9910
	13	8.075 × 10⁻³	0.20	0.59	1.00	0.9998	8.489 × 10⁻³	0.12	0.40	7.59 × 10⁻⁴	0.9982
	15	1.126 × 10⁻²	0.49	1.35	0.87	1.0000	1.359 × 10⁻²	0.21	0.46	7.60 × 10⁻⁴	0.9986
SSA850 + 4% methocel + 4% amijel + 8% starch	4	4.300 × 10⁻³	1.09	6.89	1.27	0.9830	3.981 × 10⁻³	1.02	14.38	2.89 × 10⁻⁴	0.9289
	7	7.752 × 10⁻³	3.35	8.90	1.15	0.9955	6.991 × 10⁻³	1.67	7.13	6.72 × 10⁻⁵	0.9687
	10	1.854 × 10⁻²	1.66	7.90	0.96	1.0000	1.862 × 10⁻²	1.22	5.38	1.53 × 10⁻⁴	0.9993
	13	4.781 × 10⁻²	0.75	4.33	0.77	1.0000	4.644 × 10⁻²	0.42	2.82	3.13 × 10⁻¹	0.9996
	15	5.021 × 10⁻²	0.82	3.85	0.83	0.9996	4.868 × 10⁻²	0.55	3.29	2.55 × 10⁻¹	0.9983
SSA850 + 5% methocel + 4% amijel + 8% starch	4	4.855 × 10⁻³	0.97	9.13	1.06	0.9921	4.746 × 10⁻³	3.09	37.33	4.51 × 10⁻⁴	0.9909
	7	1.260 × 10⁻²	1.15	29.54	0.81	0.9985	1.306 × 10⁻²	0.08	0.65	1.50 × 10⁻⁴	0.9894
	10	2.762 × 10⁻²	0.79	28.88	0.62	0.9974	3.043 × 10⁻²	0.09	0.29	5.00 × 10⁻⁴	0.9701
	13	7.697 × 10⁻²	0.42	1.32	0.65	1.0000	6.880 × 10⁻²	0.64	13.86	5.48 × 10⁻¹	0.9983
	15	1.231 × 10⁻¹	0.71	1.39	0.49	0.9995	1.732 × 10⁻¹	0.36	0.21	1.01 × 10⁻⁴	0.9817
SSA850 + 6% methocel + 4% amijel + 8% starch	4	4.993 × 10⁻³	0.47	8.62	0.98	0.9944	5.025 × 10⁻³	0.08	1.36	7.45 × 10⁻⁴	0.9923
	7	1.284 × 10⁻²	0.86	42.80	0.69	1.0000	1.278 × 10⁻²	0.20	5.28	3.29 × 10⁻¹	0.9979
	10	3.261 × 10⁻²	0.63	44.98	0.45	0.9968	3.190 × 10⁻²	0.19	3.67	5.89 × 10⁻¹	0.9916
	13	1.637 × 10⁻¹	0.68	3.48	0.46	0.9991	1.466 × 10⁻¹	0.42	2.20	6.86 × 10⁻¹	0.9988
	15	2.536 × 10⁻¹	1.82	0.26	2.99	0.9937	1.771 × 10⁻¹	2.75	0.80	4.43 × 10⁻⁴	0.9915

Initial value of dynamic viscosity (η 0) and activation energy calculated from Arrhenius plots of sludge systems (SS0, SSA850, SSA850 + 4% methocel + 4% amijel + 8% starch, and SSA850 + 5% methocel + 4% amijel + 8% starch) at TS = 10%

Samples	TS (%)	(η ₀) (Pa s)	E _a (kJ mol⁻¹)	R ²
SS0	10	4.29 × 10⁻⁷	20.80	0.9916
SSA850	10	1.56 × 10⁻⁴	5.10	0.9885
SSA850 + meth4%+ ami4%+ star8%	10	1.23 × 10⁻⁶	23.35	0.9939
SSA850 + meth5%+ ami4%+ star8%	10	1.11 × 10⁻⁶	24.67	0.9890

Impact of calcination temperature, organic additive percentages, and testing temperature on the rheological behaviour of dried sewage sludge

Figures & Tables

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Figure 12

Figure 13

Figure 14

Fitting parameters of different viscosity rheological models for different TS of SS0 and SSAs at 20°C

Fitting parameters of different shear stress rheological models for different TS of SSA850, mixed with organic additives (4% amijel + 8% starch) and various percentages of methocel: 3, 4, 5, and 6%, at 20°C

Chemical composition and weight LOI of SS0 and SSAs

Fitting parameters of different shear stress rheological models for different TS of SS0 and SSAs at 20°C

Fitting parameters of different viscosity rheological models for different TS of SSA, mixed with organic additives (4% methocel + 4% amijel + 8% starch), at 20°C

Fitting parameters of different viscosity rheological models for a TS = 10% of SS0, SSA850, SSA850 + 4% methocel + 4% amijel + 8% starch, and SSA850 + 5% methocel + 4% amijel + 8% starch at different testing temperatures (20, 30, 40, 50, and 60°C)

Fitting parameters of different shear stress rheological models for different TS of SSAs mixed with organic additives (4% methocel + 4% amijel + 8% starch) at 20°C

Fitting parameters of different shear stress rheological models for a TS = 10% of SS0, SSA850, SSA850 mixed with 4% methocel + 4% amijel + 8% starch, and SSA850 mixed with 5% methocel + 4% amijel + 8% starch, at different testing temperatures (20, 30, 40, 50, and 60°C)

Fitting parameters of different viscosity rheological models for different TS of SSA850, mixed with organic additives (4% amijel + 8% starch) and various percentages of methocel: 3, 4, 5, and 6%, at 20°C

Initial value of dynamic viscosity (η 0) and activation energy calculated from Arrhenius plots of sludge systems (SS0, SSA850, SSA850 + 4% methocel + 4% amijel + 8% starch, and SSA850 + 5% methocel + 4% amijel + 8% starch) at TS = 10%

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