Energetic valorization of Nador lagoon algae and proposal to use it as a means of elimination of the eutrophication in this lagoon

Highlights

• The red alga (Alsidium corallinum) produced the most biogas (85.23 ml/gVS).

• The green alga (Chaetomorpha linum) produced the least biogas (22.23 ml/g VS).

• The brown alga (Cystoseira barbata) ranked second place with 76.45 ml/gVS of biogas product.

• The three lagoon-polluting algae are green energy producers.

• We propose a new system which will halt eutrophication of this lagoon.

Abstract

The Nador lagoon is one of the best lagoons in the Mediterranean, it currently suffers from eutrophication caused by algae proliferation. In this study, we valorised the three important algae that are responsible for pollution of the lagoon. We determine their potential of biogas production and green energy capacities and we studied their effects on anaerobic bacteria proliferation in digester. After 40 days of incubation in batch mode we observed the red alga (Alsidium corallinum) produced the most biogas with 85.23 ml/gVS, which is equivalent to 511 kWh/tVS of green energy, whereas the brown alga (Cystoseira barbata) ranked second place with 76.45 ml/gVS of biogas product, the equivalent to 458 kWh/tVS of green energy. But, the green alga (Chaetomorpha linum) produced the least biogas do not exceed 22.23 ml/g VS, so these algae produces the lowest amount of energy green 133 kWh/tVS. Thus, this red alga (Alsidium corallinum) were considered excellent substrate for anaerobic digestion. These results correlated with the anaerobic bacterial proliferation of the inoculum, where the two algae (Alsidium corallinum and Cystoseira barbata) led to a large proliferation of anaerobic bacteria, from 1.8 × 10⁵ CFU/g to 61 × 10⁵ CFU/g, followed by the green alga. Therefore, we consider these three algae (Alsidium corallinum, Cystoseira barbata, and Chaetomorpha linum) as an exploitable energy reservoir in Nador lagoon. Finally, we propose that a new system which will halt eutrophication of this lagoon, it comprising anaerobic digestion of these algae, be installed to produce green energy for a lagoon aerator to dissolve the atmospheric oxygen inside the lagoon.

Introduction

The Nador Lagoon is the only lagoon ecosystem in the Moroccan coast facing the Mediterranean Sea, also called Marchica lagoon. It covers an area of 115 km² with water depths from 3 to 8 m. (El-Alami et al., 1998, Erimesco, 1961); located in the Rif region of northeast Morocco between Cape Three Forks and the Cape Water (Ramdani et al., 2015); It holds a major interest in present-day Moroccan socioeconomic and ecological (Giuliani et al., 2015, Orbi et al., 2008). This environment is exposed to a number of potential polluting sources (Maanan et al., 2015). The daily discharges of domestic, agricultural, and industrial waste into the lagoon stimulate the proliferation of algae call “harmful algal blooms” (Lapointe et al., 2015, Ruiz et al., 2006). This increases oxygen consumption due to the degradation of algae produced there causing an imbalance of this ecosystem, which leads to eutrophication (Lapointe et al., 1994, Rybarczyk et al., 1996). Several authors have examined algae proliferation as a means to evaluate the health of the lagoon. They monitored algae as bioindicators of the lagoon’s water quality (Benchekroun et al., 2013, Dokulil, 2003, Hédouin et al., 2008). However, no research has been done to determine an effective means of lagoon depollution and valorisation of these indigenous algae.

Faced with the environmental challenge to protect and valorise this natural wonder, it is necessary to develop a technology that combines the management, valorisation, and production of green energy from algae for the depollution of this lagoon. Among current technologies, anaerobic digestion, which is gaining more importance in Morocco and around the world, was chosen for this study. Anaerobic digestion is based on the degradation of various organic wastes, which are partially converted by microorganisms into biogas including methane, in hermetically sealed bioreactors (Angelidaki et al., 2003, Elasri and Afilal, 2016). Algae are again receiving attention as a substrate for anaerobic digestion by several researchers (Ghadiryanfar et al., 2016, Zhao and Ruan, 2013) mainly in Asia and Australia caused by their significant proliferation in the Pacific region causing more environmental problems but these studies are insufficient front of the big number of species that proliferates every day (Hughes et al., 2012).

The goal of this study is to propose a new approach and effective design for the remediation and recovery of these native algae in the lagoon. The objectives of this study are: 1) We sought to compare the biogas production by the three major algae that pollute the Nador lagoon (Alsidium corallinum, Cystoseira barbata, and Chaetomorpha linum); 2) We study their effects on anaerobic bacterial growth of inoculum; and 3) We estimated the potential energy produced by these algae to propose an innovative solution for treatment of the Nador lagoon. Finally, This study is the first attempt to treat the algae of this lagoon by anaerobic digestion.