A simple field essay for detecting departures from expected performance in small-scale, remote or rural wastewater treatment plants

Marcos Von Sperling,Emmanuelle Machado Maia Nogueira Lima,Mirene Augusta De Andrade Moraes

doi:10.2166/wst.2020.421

Abstract

A scientific basis is given to the traditional method of inferring effluent quality based on visualization of samples in transparent flasks. A scale of 1-6, with different printed grey intensities, is placed behind transparent PET bottles containing the sample, and gives an indication of the range of turbidity in the sample (1 is the most transparent and can only be visualized if the effluent is well clarified; in the other spectrum, 6 is the darkest and indicates highly turbid effluents). Turbidity has been correlated with total suspended solids (TSS), particulate biochemical oxygen demand (BOD) and particulate chemical oxygen demand (COD) based on thousands of monitored data collected in the effluent from seven different treatment processes in Brazil: upflow anaerobic sludge blanket (UASB) reactor, trickling filters, activated sludge, horizontal wetland, vertical wetland, polishing ponds and coarse filter after pond. The method is simple and instantaneous, can be used in virtually all places and in every visit of the operator to the remote treatment plant, allows recording of the image in smartphones, does not use any equipment, chemicals or energy, and has been showed to represent well the effluent quality of existing treatment plants. This essay is complementary and does not substitute specific traditional sampling and analysis, but allows easy inference of deterioration of effluent quality.

Highlights

In small wastewater treatment plants (WWTP) and in localities in rural or remote areas, effluent quality monitoring is usually performed at very low frequencies and it is not uncommon to have plants with no samples collected and analysed over a long period
The operator may be in doubt in the selection between one stripe or the adjacent one, but this uncertainty is believed not to alter the key message that needs to be passed: is the plant working as expected or is the performance departure mild or severe? Assuming that a photographic recording will be made at every visit of the operator to the treatment plant, robustness is achieved by having a large number of samples per month or year, and not based on a single evaluation
The Grey Scale consists of six stripes in ascending order of transparency of grey, which are linked to the clarification level of the effluent

Summary

Introduction

In small wastewater treatment plants (WWTP) and in localities in rural or remote areas, effluent quality monitoring is usually performed at very low frequencies and it is not uncommon to have plants with no samples collected and analysed over a long period. One should question the reliability of the interpretation of very small datasets that do not have the potential to sustain statistical evaluations (Oliveira ; von Sperling et al ). These limitations are identified in Brazil (von Sperling ), the country of residence of the authors, but are characteristic in Latin America, due to the prevalence of small-sized treatment plants (Noyola et al ), and, to a larger extent, to developing countries in general, when facing the challenge of complying with regulatory standards (Johnstone & Norton ). It should be understood that, when necessary, microbiological and physical-chemical analysis, together with other specific experimental methods, can be used in order to enhance the understanding of the behaviour of the treatment plant (Van Loosdrecht et al ; Lourenço & Nunes )

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