Sewage Treatment System

3.5.3 Sewage Treatment System

In living quarter platforms that have a large volume of sewage material, to dilute it to an acceptable limit a large volume of freshwater is required. The main portion of solids may be filtered. This is either burned in an incinerator or kept in another tank to be transported onshore via supply boats. The remaining materials will be discharged via sewage caisson to sea. In many platforms this is a nutrition point for fishes. It is normal to have fish colonies gathering around these points.

Tanks can be made of mild carbon steel. Only hypochlorite tank shall be of suitable material such as plastic or GRP to prevent corrosion.

A macerator will disintegrate solids to a smaller size before being diluted with freshwater. Therefore it shall have a hardened surface to resist wearing of its internal surfaces.

Package capacity depends on the number of personnel on the platform. For unmanned platforms that are only visited by a limited number of crew during maintenance, a minimum capacity will be specified. For others, 100 to 150 L/day for each crew may be used.

11.05.3.4 Effluent Monitoring

Reducing mercury in the environment has been a top priority not only for MWRA, but also for policymakers throughout New England and Canada. Mercury accumulation in fish is a major source to humans, and most water bodies in Massachusetts are subject to fish consumption advisories due to mercury. Through MWRA’s source-reduction program, approximately 75% of dentists in the region installed amalgam separators to reduce mercury inputs to the sewer system, and hospitals are reducing mercury discharges. Loads in the influent, effluent, and fertilizer pellets made from biosolids show large declines. Influent loads have been cut in half since 1999. Mercury discharges in the effluent have decreased from an average of 0.14 lb d⁻¹ in 1999 to 0.03 lb d⁻¹ in 2008. Now, most of the mercury entering Massachusetts water bodies originates from air pollution generated by power plants in the Midwest and Southeast.

2.5 Sewage sludge: A challenge that needs to grow

The management and final disposal of biosolids from wastewater treatment processes is a growing concern in Brazil as sewage treatment systems are effectively implemented and operated. Planning the management of biosolids by providing forms of disposal that do not depend on landfills will be technically, environmentally, and economically necessary to enable universal sanitation.

There is no inventory on sludge management technologies in Brazil as detailed as ANA's surveys. But the most common alternatives are conventional drying beds for small and medium-sized WWTPs, and mechanical dewatering equipment (centrifuges, screw press, etc.) for medium and large WWTPs. Two other important applications are dewatering bags and alkaline stabilization. The destination of biosolids to landfills is still the main form of final disposal; however, there are important cases of agricultural disposal of sludge conducted by the state sanitation companies of São Paulo, Federal District, and Paraná (Sampaio, 2013).

Of the various alternatives for the proper disposal of sewage sludge, agricultural recycling is the most promising both from an environmental and an economic aspect, as it transforms waste into an important agricultural input. In 2010, some 42% of Europe's municipal sewage sludge was treated and used on farmland, 27% was incinerated, 14% was disposed of by landfilling, and about 17% was disposed of in other ways, according to Eurostat (Eurostat, 2015).

The economic benefits from recycling nutrients and organic matter from sludge should also be highlighted. Studies by Corrêa and Corrêa (2001) suggest that the nitrogen, phosphorus, and organic matter present in a ton of fresh sewage sludge can represent values in the order of R $ 22.00 per ton. These values can reach R$ 31.00 per ton and R$ 158.00 per ton for composted and thermally dried sludge, respectively.

Agricultural sludge recycling in Brazil is well established in some regions. SANEPAR, Paraná’s sanitation company, is the national leader, with a long history of research and practices. SABESP, from São Paulo, and CAESB, from the Federal District, are also companies with extensive experience. It is important to emphasize the established experiences with energy recovery from sludge in some larger treatment plants. Arrudas WWTP (Belo Horizonte—MG) and Belém WWTP (Curitiba—PR) are widely known cases.

But despite these important national experiences, there is still a huge demand for improvement and expansion, once sewage treatment infrastructure is expected to grow and traditional sludge management approaches face technical and economic barriers, given Brazilian geographic characteristics. Operational complexity and high CAPEX and OPEX make it difficult to use mechanized systems in small and medium-sized municipalities. Another important factor is the viability scale for some technologies, such as energy recovery and mechanical composting. These two approaches tend to be viable in larger municipalities, with populations over 100,000 inhabitants, once scalability and financial sustainability are linked not only to technical aspects, but also to market strategies. Finally, another limitation of landfill disposal, disregarding environmental aspects, is the scarcity of such structures, especially in small size municipalities.

Two other important regulatory frameworks are the National Solid Waste Policy (Brasil, 2010) and the National Climate Change Policy (Brasil, 2009a). Both public policies drive the sewage treatment sector toward better energy efficiency, reduction of operating costs, and improvements in sludge management. Thus, the Brazilian technological matrix requires approaches to sludge management that address these technical, economic, and environmental challenges. In this scenario, constructed wetlands systems are emerging with enormous potential to meet these demands.

11.2.2 Septic Systems

Septic systems for subsurface disposal of human wastewater are the rule in more rural areas not served by sewers and sewage treatment systems. Most septic systems serve a single household, but some larger systems serve a cluster of homes and/or offices.

Wastewater contains dissolved organic compounds that fuel redox reactions in microbes that live in the system. Redox reactions in the tank are usually anaerobic, including fermentation, methane generation, and sulfate reduction (Wilhelm et al., 1994). The water leaving the tank has high concentrations of organic compounds, CO₂, and ammonium (NH${}_4^{+}$).

In the leaching field, oxygen is available and aerobic respiration and nitrification are the key processes (Table 10.13). The concentrations of organic compounds and NH${}_4^{+}$ decrease, CO₂ is evolved, and the nitrate (NO${}_3^{-}$) concentration increases. It is typical for effluent leaving the unsaturated zone of a properly functioning leaching field to have nitrate concentrations in the range of 20 to 70 mg/L (NO${}_3^{-}$–N: mass of nitrogen in nitrate per volume), which exceeds the U.S. drinking water maximum contaminant level (MCL) of 10 mg/L (NO${}_3^{-}$–N). In most septic systems, nitrate is a groundwater contaminant of concern. Some septic system designs include another anaerobic zone beyond the aerobic zone in the leaching field, where denitrification (Table 10.13) reduces nitrate concentrations in the effluent (Robertson and Cherry, 1995; Robertson et al., 2000).

It has recently come to light that wastewater effluent from commercial and household disposal systems can also contain a range of chemical compounds found in medications, food, personal care products, and household products (Kolpin et al., 2002; Standley et al., 2008). Chemicals in medications and food pass through humans and persist in the system effluent. For example, caffeine has been used as an indicator of septic system contamination (Seiler et al., 1999). Hormones are particularly troubling chemicals that persist long enough to migrate through the disposal system to groundwaters and surface waters, where they can harm aquatic life. In Cape Cod, Massachusetts, where over 85% of homes have septic systems, several ponds in the sand and gravel aquifer contained estrogenic hormones at concentrations approaching those known to induce physiological responses in fish (Standley et al., 2008).

Septic systems fail when the leaching field doesn't have enough access to oxygen to fully degrade the organic carbon with aerobic respiration. This can happen when the system is placed too close to the water table, in soils that are too fine grained, or in old systems that become clogged with a biological mat that remains saturated.

Environmental Fate and Behavior

The use of surfactants in household, industrial, and institutional cleaning products mostly implies environmental emissions through the drain into wastewater treatment systems (sewage treatment plants or septic tank systems) and aquatic systems. The hydrocarbon chains of these materials generally tend to break down in the environment relatively quickly. The business end of the molecule behaves differently; hence, no overarching statements can be made. Sodium lauryl sulfate can readily be removed from aqueous systems (filtering and aeration) and is readily biodegraded (42 out of 45 Pseudomonas strains could degrade alkyl sulfates to saturated and unsaturated fatty acids). In sewage, sludge, seawater, and in selected organisms from 75 to 100%, degradation is reported for sodium lauryl sulfate. Several jurisdictions, including the US and the EU, have regulatory requirements regarding the biodegradability of surfactants.

2.5.3 Migration and transformation of other HRPs in wastewater

DBPs are usually produced during the final process of disinfection of the water treatment, so the disinfection by-products generated are no longer discharged directly into the downstream water body through the sewage treatment system.

Generally, due to the non-biodegradability, nano-material cannot be degraded in sewage treatment system based biological treatment technology. Absorption is the main removal route for nano-material in wastewater treatment system. Kiser et al. (2009) investigated the removal and release of titanium in WWTPs and found that the sample containing 2250 mg/L TSS had approximately 85% for Ti.

Regarding microplastics, the overall microplastics removal efficiencies of WWTPs without tertiary treatment were above 88% and the number increased to over 97% in the WWTPs with tertiary treatment. The relatively high removal efficiency of microplastics by WWTPs indicated that most microplastics were retained in the sewage sludge (Sun et al., 2019).

3.6.3.1 Medical and pharmaceutical wastewater

Medical and pharmaceutical wastewater contains a large amount of ARGs and ARB, which is the main source of ARGs and ARB in the water environment. Rodriguez-Mozaz et al. (2015) have detected ARGs in hospital sewage, urban sewage treatment system, and the receiving river in Spain, and found that the abundances of bla_TEM, qnrS, sulI, and tet(W) in hospital sewage were higher than those in the urban sewage treatment system and the receiving river. ARGs within β-lactam (bla_VIM and bla_SHV), aminoglycosides (aacC2), chloramphenicol (catA1 and floR), macrolide–lincosamide–streptogramins (emrA and mefA), sulfonamide (sulI and sulII), and tetracycline (tet(A), tet(B), tet(C), tet(O), and tet(W)) associated with transposons have been found in Romanian hospital sewage (Szekeres et al., 2017). In addition, sulfonamide (sulI and sulII)), tetracycline (tet(O), tet(T), tet(M), tet(Q), and tet(W), β-lactam (bla_OXA-1, bla_OXA-2, and bla_OXA-10), and macrolide (ermB) resistance genes were detected based on quantitative PCR analysis in typical pharmaceutical wastewater treatment systems (Zhai et al., 2016). The maximum concentrations of ARGs detected in the final effluents of pharmaceutical WWTPs were up to 3.68 × 10⁶ copies/mL by Wang et al. (2015) and 2.36 × 10⁷ copies/mL by Zhai et al. (2016), respectively, which were much higher than the concentration in MWTPs as revealed by Mao et al. (2015).

In hospital sewage in New Delhi, Lamba et al. (2017) have detected 748 extended-spectrum β-lactam resistant bacterial strains (including Escherichia coli, Klebsiella, and Pseudomonas putida) and 953 carbapenem-resistant Enterobacteriaceae strains (including Klebsiella pneumoniae, Pseudomonas putida, and Klebsiella pneumonia subsp. Pneumonia). ARB resistant to carbapenem also existed in hospital sewage in China, Croatia, and other countries in the world (Zhang et al., 2013a; Hrenovic et al., 2015).

3.9.4 Fluorescent Whitening Agents

Several studies have used FWAs as indicators of fecal contamination (Boving et al., 2004, Gilpin et al., 2002, Hayashi et al., 2002) and with other measures were successful in differentiating sources.