Investigation of direct waste‐activated sludge dewatering benefits and costs in a water resource recovery facility

Abstract

Dewatering of anaerobic digested (AD) sludge containing waste‐activated sludge (WAS) from enhanced biological phosphorus removal (EBPR) poses numerous challenges including poor dewaterability, struvite scale formation, and recycling of high N and P levels in the sludge liquor to the treatment process. A full‐scale water reclamation facility was investigated to mitigate these problems by experimenting with direct dewatering of EBPR WAS, bypassing the AD step. The investigations experimented with various blends of AD primary sludge with undigested thickened WAS to achieve dewatering performance improvements and overall operational cost savings. Direct thickened WAS dewatering has had many positive impacts including enhanced sludge cake solids concentration, reduced chemical use for facility operations, reduced struvite scaling, reduced biogas conditioning media servicing, eliminated need for centrate treatment, recovered capacity of existing unit operations including anaerobic digesters, and eliminated several proposed capital improvement projects that were previously deemed necessary. Although bypassing of WAS to AD reduced total biogas production, the specific gas yield increased to meet all of the facility's biogas demands and minimized excess gas flaring. The overall biosolids production mass increased causing increased transportation costs for disposal and caused notable odors, both of which are being currently investigated. Practitioner Points Direct WAS dewatering bypassing anaerobic digestion yields operational and process benefits in an EBPR water resource recovery facility Dewatered cake solids were increased compared with combined primary and WAS anaerobic digestion and dewatering Nutrient loads in sludge processing returns streams and operational costs are reduced by direct WAS dewatering

Mini-review of inventory data for the dewatering and drying of sewage sludge

“…During dewatering, some of the soluble compounds and fine particulate matter will leave along with the water being removed. This is supported by data reported on the liquid fraction of digestate, revealing ranges of 240–5630 mg solids L −1 (Mailler et al, 2021; Mentzer et al, 2021; Sun et al, 2021). Mailler et al (2021) reported high phosphorus (P: 71 mg L −1 ) and ammonium concentrations (NH 4 + : 389 mg L −1 ) in the liquid fraction.…”

Clarifying the Role of Phosphorus Management Strategies in Enhancing the Sustainability of Wastewater Treatment Plants

“…Phosphorus removal processes have a direct impact on sludge dewatering properties. In terms of EBPR process, the impacts on sludge dewatering are clear and wellestablished [79,80]. Generally, sludge from the EBPR process is more difficult to dewater [80].…”

“…In terms of EBPR process, the impacts on sludge dewatering are clear and wellestablished [79,80]. Generally, sludge from the EBPR process is more difficult to dewater [80]. Phosphorus release during sludge treatment is accompanied by the release of cations, of which the divalent ions are then deposited quickly.…”

“…This results in an increase in the ratio of monovalent cations to divalent cations, leading to a deterioration in sludge dewatering performance. On the other hand, the polyphosphates adsorbed on extracellular polymeric substances (EPS) increase the quantity of bound water, making it more difficult to remove in the dewatering process [80][81][82]. Therefore, sludge from the EBPR process generally requires a higher dosage of flocculant dosage to enhance dewatering efficiency.…”

Pathways to Water Sector Decarbonization, Carbon Capture and Utilization

“…A case study which investigated an alternative sludge treatment processing strategy which led to whole plant chemical use reduction and operating cost reduction was described by Mentzer et al (2021). The major goal of this study was to enhance the dewaterability of final sludge being sent to a landfill for disposal.…”