Process schemes for future energy-positive water
resource recovery facilities
Kimberly Solon , Mingsheng Jia and Eveline I. P. Volcke
ABSTRACT
There are numerous successful studies on optimizing the performance of conventional activated
sludge (CAS)-based wastewater treatment plants. However, recent studies have shown that a more
significant improvement of the plant performance is achievable through integration of established
technologies in novel process schemes. High-rate activated sludge system, chemically enhanced
primary treatment, partial nitritation-anammox, partial nitrification-denitrification over nitrite and
anaerobic digestion are integrated in two process schemes to determine to which extent energy
savings and energy production can be achieved with these new process layouts compared to a
CAS-based process scheme. The results presented in this paper show that there is potential for
achieving future energy-positive water resource recovery facilities through novel integration of
mature technologies for municipal wastewater treatment.
Kimberly Solon (corresponding author)
Mingsheng Jia
Eveline I. P. Volcke
Biosystems Control (BioCo) Research Group,
Department of Green Chemistry and
Technology,
Ghent University,
Coupure links 653, 9000 Ghent,
Belgium
E-mail: kimberly.solon@ugent.be
Key words | chemically enhanced primary treatment, energy recovery, high rate activated sludge,
partial nitritation-anammox, partial nitrification-denitrification over nitrite
INTRODUCTION
A strategy for organics (commonly measured as chemical
oxygen demand, COD) removal and energy recovery is to
think of organics in terms of their energy content. A typical
municipal wastewater contains an average of 0.5 kg COD·m
3
(McCarty et al. ) and an associated calorific energy
content of potentially at least 4 kWh·kg
1
COD (Heidrich
et al. ; Jenicek et al. ); that is, 2 kWh·m
3
of waste-
water. As around 0.45–0.60 kWh·m
3
(McCarty et al. ;
Wan et al. ) is required for a conventional wastewater
treatment plant that employs an activated sludge system
and anaerobic digestion (AD), this implies that optimizing
energy recovery from the COD content of the wastewater
could result in an overall energy-neutral or even energy-
positive facility. Moreover, considering that aeration costs
in a water resource recovery facility (WRRF) account for a
substantial 45–75% of the overall operating costs of the
facility (Rosso et al. ), recovering energy through COD
redirection in the primary treatment stages could positively
impact the operational cost by reducing the aeration
energy requirements for aerobic COD removal.
Energy savings of up to 10% in blowers and 50%
in recirculation pumps was simulated as feasible using an
ammonium-based supervisory control system (Serralta
et al. ). Rieger et al. () demonstrated that up to
20% decrease in total energy requirements can be achieved
(30% in simulations) besides an improved effluent quality
upon implementing full-scale dissolved oxygen (DO)-based
and ammonia (NH
3
)-based aeration control strategies. An
overview of aeration control systems applied to municipal
WRRFs revealed as high as 27% aeration energy require-
ment reduction for a full-scale activated sludge process
(Åmand et al. ), while optimization of aeration control
strategies combined with electricity production and on-site
utilization from AD biogas has been shown to achieve 30–
50% reduction in energy costs (Wett et al. ). However,
these values suggest that, with aeration control strategies
and conventional CAS-based layout alone, a fully energy
self-sufficient WRRF will not be achieved unless external
resources are added, such as organic wastes for co-digestion
(Shen et al. ), or by modifying plant layouts and incor-
porating other unit processes (Khiewwijit et al. ;
Fernández-Arévalo et al. ).
To become energy self-sufficient or even energy-positive,
WRRFs are examining the application of unit processes,
1808 © IWA Publishing 2019 Water Science & Technology | 79.9 | 2019
doi: 10.2166/wst.2019.183
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