Advances in Wastewater Treatment

Giorgio Mannina, G. A. Ekama, Hallvard Ødegaard, Gustaf Olsson, Giorgio Mannina, G. A. Ekama, Hallvard Ødegaard, Gustaf Olsson

• Editore: IWA Publishing
• Anno: 2018
• ISBN:
  9781780409726
• Argomento: Biowissenschaften
• Categoria: Umweltwissenschaft

Advances in Wastewater Treatment presents a compendium of the key topics surrounding wastewater treatment, assembled by looking at the future technologies, and provides future perspectives in wastewater treatment and modelling. It covers the fundamentals and innovative wastewater treatment processes (such as membrane bioreactors and granular process). Furthermore, it focuses attention on mathematical modelling aspects in the field of wastewater treatments by highlighting the key role of models in process design, operation and control.Other topics include: • Anaerobic digestion• Biological nutrient removal• Instrumentation, control and automation• Computational fluid dynamics in wastewater• IFAS systems• New frontiers in wastewater treatment• Greenhouse gas emissions from wastewater treatmentEach topic is addressed by discussing past, present and future trends. Advances in Wastewater Treatment is a valid support for researchers, practitioners and also students to have a frame of the frontiers in wastewater treatment and modelling.

© IWA Publishing 2018. Giorgio Mannina, George Ekama, Hallvard Ødegaard and Gustaf Olsson. Advances in Wastewater Treatment DOI: 10.2166/9781780409719_0001

Chapter 1

Primary treatment: Particle separation by rotating belt sieves

B. Rusten1 and H. Ødegaard2

1Aquateam COWI, Oslo, Norway

2Hallvard Ødegaard, Scandinavian Environmental Technology and NTNU, Trondheim, Norway (SET AS, Hellemsveien 421, N 7165 Oksvoll, Norway)

ABSTRACT

Fine mesh rotating belt sieves (RBSs) offer a compact solution for removal of particles in primary treatment of wastewater. This chapter shows examples from lab-scale, pilot-scale and full-scale testing of primary treatment and chemically enhanced primary treatment (CEPT). In a Norwegian full-scale survey, the use of a 350 µm belt showed more than 40% removal of total suspended solids (TSS) and 30% removal of chemical oxygen demand (COD) at sieve rates as high as 160 m3 ⋅ m−2 ⋅ h−1. Maximum sieve rate tested was 288 m3 ⋅ m−2 ⋅ h−1 and maximum particle load was 80 kg TSS ⋅ m−2 ⋅ h−1. When the sludge mat on the belt increased from 10 to 55 g TSS ⋅ m−2, the removal efficiency for TSS increased from about 35 to 60%. CEPT is a simple and effective way of increasing the removal efficiency of an RBS. When adding about 0.7–1.0 g ⋅ m−3 of cationic polymer and using about 2 min of flocculation time, the removal of TSS typically increased from 40–50% without polymer to 60–75% with polymer. The particulate organic matter that was removed in the RBS had little or no effect on the denitrifying capacity of the wastewater. The high volatile solids (VS) content of the RBS sludge as compared to primary clarifier sludge, gave a higher methane potential in anaerobic digesters for the RBS sludge. The high caloric value of RBS sludge makes it attractive for incineration.

Keywords: Municipal wastewater, primary treatment, rotating belt sieves

1.1 INTRODUCTION

Traditionally primary treatment has been synonymous with settling in clarifiers. Primary settling may be used as the only treatment when discharging to the ocean, or as pretreatment in order to lower the load and sludge production of subsequent more advanced treatment processes. Depending on the raw water characteristics, removal efficiencies of primary settling typically range from 40–60% with respect to total suspended solids (TSS) and 15–30% with respect to biochemical oxygen demand (BOD5).

In order to improve the separation efficiency of primary clarifiers, chemically enhanced primary treatment (CEPT) may also be used. This implies addition of coagulants and introduction of flocculation tanks ahead of the clarifier so that colloidal, non-settleable particles may be removed in addition to the suspended, settleable ones. If an inorganic coagulant is used (Al or Fe), phosphate removal is achieved as well, and in many cases this is the main purpose of using CEPT. Lately, however, focus has been on the enhanced removal of organic matter as pretreatment before de-ammonification processes (Water Environment Research Foundation [WERF], 2014; Ødegaard, 2016). Again depending on the raw water characteristics but also design and operation of coagulant mixing and flocculation, removal efficiencies of CEPT range from 70–90% with respect to TSS and 60–80% with respect to BOD5 (Ødegaard, 1992, 2016).

Clarifiers require quite a lot of space and, since low foot-print of wastewater treatment plants has become a goal in many instances, fine mesh sieves have been introduced as an alternative to settling for primary treatment. Particularly rotating belt sieves (RBSs), also referred to as rotating belt filters (RBFs), have gained popularity. In this chapter we shall focus on the development and the experiences of rotating belt sieves for primary treatment. An overview of the RBS technology will be given, as well as examples of test results from different types of applications. These are mainly based on a R&D programme on primary treatment that was carried out in 2005 (Ødegaard, 2005; Rusten & Ødegaard, 2006) and on recent experiments at municipal wastewater treatment plants in Norway (Paulsrud et al., 2014; Rusten et al., 2017; Sahu et al., 2017). A bench-scale procedure for choosing mesh size and evaluating potential treatment results is also presented (Rusten & Ødegaard, 2006).

1.1.1 The Norwegian primary treatment evaluation programme

Due to the European Union (EU) requirements for wastewater treatment, the Norwegian State Pollution Control Agency (SFT) took an initiative to evaluate and test several different technologies for primary treatment. This R&D programme was carried out with contributions from research institutions (NTNU, SINTEF and NIVA), consulting companies (Asplan Viak, Rambøll and Aquateam), the cities of Bergen and Tromsø, and the regional water and wastewater utility company IVAR (Ødegaard, 2005).

The goal was to find dependable and cost-efficient technologies that fulfilled the EU criteria for primary treatment, i.e. at least 20% removal of organic matter (measured as BOD5) and 50% removal of total suspended solids (TSS). For treatment plants >10,000 pe (population equivalent), with 24 control samples per year, at least 21 samples must fulfil the requirements. This is a lot stricter than looking at average removal efficiencies and the R&D programme showed that an average TSS-removal of about 65% was necessary for enough samples to pass the 50% removal requirement.

Several types of primary treatment options, such as clarifiers, fine mesh sieves, large septic tanks, dissolved air flotation (DAF) and deep bed filtration were initially evaluated. Of the technologies that were considered fully developed, clarifiers and different types of fine mesh sieves were found most suitable for primary treatment. These technologies were then tested in full scale at several treatment plants, for both primary treatment and chemically enhanced primar...